bpf: Add atomic compare-and-exchange instructions

This patch adds the two remaining BPF v3 atomic instructions:
- BPF_INSN_ACMP{,32}: atomic compare-and-swap
- BPF_INSN_AXCHG{,32}: atomic (non-conditional) exchange

Tests and documentation are also updated.

gas/
	* doc/c-bpf.texi (BPF Instructions): Document atomic exchange and
	atomic compare-and-swap instructions.
	* testsuite/gas/bpf/atomic.s: Test ACMP, ACMP32, AXCHG, AXCGH32
	instructions.
	* testsuite/gas/bpf/atomic.d: Likewise.
	* testsuite/gas/bpf/atomic-be.d: Likewise.
	* testsuite/gas/bpf/atomic-pseudoc.s: Likewise.
	* testsuite/gas/bpf/atomic-pseudoc.d: Likewise.
	* testsuite/gas/bpf/atomic-be-pseudoc.d: Likewise.

include/
	* opcode/bpf.h (BPF_IMM32_ACMP): Fix typo.
	(enum bpf_insn_id): New entries for BPF_INSN_ACMP{,32} and
	BPF_INSN_AXCHG{,32}.

opcodes/
	* bpf-opc.c (bpf_opcodes): Add entries for ACMP{,32} and
	AXCHG{,32} instructions.

include/opcode/bpf.h

@@ -153,7 +153,7 @@ typedef uint64_t bpf_insn_word;
 #define BPF_IMM32_AFAND ((uint64_t)0x00000051)
 #define BPF_IMM32_AFXOR ((uint64_t)0x000000a1)
 #define BPF_IMM32_AXCHG ((uint64_t)0x000000e1)
-#define BPF_IMM32_ACMP  ((uint64_t)b0x000000f1)
+#define BPF_IMM32_ACMP  ((uint64_t)0x000000f1)
 
 /* Unique identifiers for BPF instructions.  */
 
@@ -225,6 +225,10 @@ enum bpf_insn_id
   BPF_INSN_AADD32, BPF_INSN_AOR32, BPF_INSN_AAND32, BPF_INSN_AXOR32,
   /* Atomic instructions with fetching (32-bit.)  */
   BPF_INSN_AFADD32, BPF_INSN_AFOR32, BPF_INSN_AFAND32, BPF_INSN_AFXOR32,
+  /* Atomic compare-and-swap, atomic exchange.  */
+  BPF_INSN_ACMP, BPF_INSN_AXCHG,
+  /* Atomic compare-and-swap, atomic exchange (32-bit).  */
+  BPF_INSN_ACMP32, BPF_INSN_AXCHG32,
   /* GNU simulator specific instruction.  */
   BPF_INSN_BRKPT,
 };