MIPS: default r6 if vendor is img

This behavior is used by downstream toolchain since 2014.
We also set the default ABI for mips*-img-elf to O32.
The previous value is NO_ABI, which is not good default ABI.

We don't support mips64*-img* due to GCC doesn't support it,
and We believe that the multilib should be used for this case.

bfd/config.bfd

@@ -1537,7 +1537,7 @@ case "${targ_defvec} ${targ_selvecs}" in
 esac
 
 case "${targ}" in
-  mipsisa32r6* | mipsisa64r6*)
+  mipsisa32r6* | mipsisa64r6* | mips*-img-*)
     targ_cflags="$targ_cflags -DMIPS_DEFAULT_R6=1"
     ;;
 esac

gas/configure

@@ -12211,6 +12211,12 @@ _ACEOF
 	    use_e_mips_abi_o32=1
 	    ;;
 	esac
+	# If Vendor is IMG, then MIPSr6 is used
+	case ${target} in
+	  mips*-img-*)
+	    mips_cpu=mips32r6
+	    ;;
+	esac
 	# Decide whether to generate 32-bit or 64-bit code by default.
 	# Used to resolve -march=from-abi when an embedded ABI is selected.
 	case ${target} in
@@ -12230,7 +12236,7 @@ _ACEOF
 	  | mips64*-kfreebsd*-gnu | mips64*-ps2-elf*)
 	    mips_default_abi=N32_ABI
 	    ;;
-	  mips*-linux* | mips*-freebsd* | mips*-kfreebsd*-gnu)
+	  mips*-linux* | mips*-freebsd* | mips*-kfreebsd*-gnu | mips*-img-elf)
 	    mips_default_abi=O32_ABI
 	    ;;
 	  mips64*-openbsd*)

gas/configure.ac

@@ -380,6 +380,12 @@ changequote([,])dnl
 	    use_e_mips_abi_o32=1
 	    ;;
 	esac
+	# If Vendor is IMG, then MIPSr6 is used
+	case ${target} in
+	  mips*-img-*)
+	    mips_cpu=mips32r6
+	    ;;
+	esac
 	# Decide whether to generate 32-bit or 64-bit code by default.
 	# Used to resolve -march=from-abi when an embedded ABI is selected.
 	case ${target} in
@@ -399,7 +405,7 @@ changequote([,])dnl
 	  | mips64*-kfreebsd*-gnu | mips64*-ps2-elf*)
 	    mips_default_abi=N32_ABI
 	    ;;
-	  mips*-linux* | mips*-freebsd* | mips*-kfreebsd*-gnu)
+	  mips*-linux* | mips*-freebsd* | mips*-kfreebsd*-gnu | mips*-img-elf)
 	    mips_default_abi=O32_ABI
 	    ;;
 	  mips64*-openbsd*)