[binutils, ARM, 1/16] Add support for Armv8.1-M Mainline CLI

The patch is straightforward, it does the following:

- support the new Tag_CPU_arch build attribute value, ie.:
   + declare the new value
   + update all the asserts forcing logic to be reviewed for new
     architectures
   + create a corresponding bfd_mach_arm_8_1M_MAIN enumerator in bfd and
     add mapping from Tag_CPU_arch to it
   + teach readelf about new Tag_CPU_arch value
- declare armv8.1-m.main as a supported architecture value
- define Armv8.1-M Mainline in terms of feature bits available
- tell objdump mapping from bfd_mach_arm_8_1M_MAIN enumerator to feature
   bits available
- update architecture-specific logic in gas and bfd guarded by the
   asserts mentioned above.
- tests for all the above

ChangeLog entries are as follows:

*** bfd/ChangeLog ***

2019-04-15  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* archures.c (bfd_mach_arm_8_1M_MAIN): Define.
	* bfd-in2.h: Regenerate.
	* cpu-arm.c (arch_info_struct): Add entry for Armv8.1-M Mainline.
	* elf32-arm.c (using_thumb_only): Return true for Armv8.1-M Mainline
	and update assert.
	(using_thumb2): Likewise.
	(using_thumb2_bl): Update assert.
	(arch_has_arm_nop): Likewise.
	(bfd_arm_get_mach_from_attributes): Add case for Armv8.1-M Mainline.
	(tag_cpu_arch_combine): Add logic for Armv8.1-M Mainline merging.

*** binutils/ChangeLog ***

2019-04-15  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* readelf.c (arm_attr_tag_CPU_arch): Add entry for Armv8.1-M Mainline.

*** gas/ChangeLog ***

2019-04-15  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* config/tc-arm.c (cpu_arch_ver): Add entry for Armv8.1-M Mainline
	Tag_CPU_arch build attribute value.  Reindent.
	(get_aeabi_cpu_arch_from_fset): Update assert.
	(aeabi_set_public_attributes): Update assert for Tag_DIV_use logic.
	* testsuite/gas/arm/attr-march-armv8_1-m.main.d: New test.

*** include/ChangeLog ***

2019-04-15  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* elf/arm.h (TAG_CPU_ARCH_V8_1M_MAIN): new macro.
	(MAX_TAG_CPU_ARCH): Set value to above macro.
	* opcode/arm.h (ARM_EXT2_V8_1M_MAIN): New macro.
	(ARM_AEXT_V8_1M_MAIN): Likewise.
	(ARM_AEXT2_V8_1M_MAIN): Likewise.
	(ARM_ARCH_V8_1M_MAIN): Likewise.

*** ld/ChangeLog ***

2019-04-15  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* testsuite/ld-arm/attr-merge-13.attr: New test.
	* testsuite/ld-arm/attr-merge-13a.s: New test.
	* testsuite/ld-arm/attr-merge-13b.s: New test.

*** opcodes/ChangeLog ***

2019-04-15  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* arm-dis.c (select_arm_features): Add logic for Armv8.1-M Mainline.

include/opcode/arm.h

@@ -72,6 +72,7 @@
 #define ARM_EXT2_V8_5A	     0x00001000	/* ARM V8.5A.			     */
 #define ARM_EXT2_SB	     0x00002000	/* Speculation Barrier instruction.  */
 #define ARM_EXT2_PREDRES     0x00004000	/* Prediction Restriction insns.     */
+#define ARM_EXT2_V8_1M_MAIN  0x00008000 /* ARMv8.1-M Mainline.		     */
 
 /* Co-processor space extensions.  */
 #define ARM_CEXT_XSCALE	     0x00000001	/* Allow MIA etc.	 	   */
@@ -175,6 +176,9 @@
 #define ARM_AEXT2_V8M_MAIN_DSP	 ARM_AEXT2_V8M_MAIN
 #define ARM_AEXT_V8R		 ARM_AEXT_V8A
 #define ARM_AEXT2_V8R		 ARM_AEXT2_V8AR
+#define ARM_AEXT_V8_1M_MAIN	 ARM_AEXT_V8M_MAIN
+#define ARM_AEXT2_V8_1M_MAIN	(ARM_AEXT2_V8M_MAIN | ARM_EXT2_V8_1M_MAIN     \
+						    | ARM_EXT2_FP16_INST)
 
 /* Processors with specific extensions in the co-processor space.  */
 #define ARM_ARCH_XSCALE	ARM_FEATURE_LOW (ARM_AEXT_V5TE, ARM_CEXT_XSCALE)
@@ -353,6 +357,8 @@
 #define ARM_ARCH_V8M_MAIN_DSP  ARM_FEATURE_CORE (ARM_AEXT_V8M_MAIN_DSP,	   \
 						 ARM_AEXT2_V8M_MAIN_DSP)
 #define ARM_ARCH_V8R	       ARM_FEATURE_CORE (ARM_AEXT_V8R, ARM_AEXT2_V8R)
+#define ARM_ARCH_V8_1M_MAIN    ARM_FEATURE_CORE (ARM_AEXT_V8_1M_MAIN,	   \
+						 ARM_AEXT2_V8_1M_MAIN)
 
 /* Some useful combinations:  */
 #define ARM_ARCH_NONE	ARM_FEATURE_LOW (0, 0)