cpu,opcodes: add instruction semantics to bpf.cpu and minor fixes

cpu,opcodes: add instruction semantics to bpf.cpu and minor fixes

This patch adds semantic RTL descriptions to the eBPF instructions
defined in cpu/bpf.cpu.  It also contains a couple of minor
improvements.

Tested in bpf-unknown-none targets.
No regressions.

cpu/ChangeLog:

2020-05-28  Jose E. Marchesi  <jose.marchesi@oracle.com>
	    David Faust <david.faust@oracle.com>

	* bpf.cpu (define-alu-insn-un): Add definitions of semantics.
	(define-alu-insn-mov): Likewise.
	(daib): Likewise.
	(define-alu-instructions): Likewise.
	(define-endian-insn): Likewise.
	(define-lddw): Likewise.
	(dlabs): Likewise.
	(dlind): Likewise.
	(dxli): Likewise.
	(dxsi): Likewise.
	(dsti): Likewise.
	(define-ldstx-insns): Likewise.
	(define-st-insns): Likewise.
	(define-cond-jump-insn): Likewise.
	(dcji): Likewise.
	(define-condjump-insns): Likewise.
	(define-call-insn): Likewise.
	(ja): Likewise.
	("exit"): Likewise.
	(define-atomic-insns): Likewise.
	(sem-exchange-and-add): New macro.
	* bpf.cpu ("brkpt"): New instruction.
	(bpfbf): Set word-bitsize to 32 and insn-endian big.
	(h-gpr): Prefer r0 to `a' and r6 to `ctx'.
	(h-pc): Expand definition.
	* bpf.opc (bpf_print_insn): Set endian_code to BIG.

opcodes/ChangeLog:

2020-05-28  Jose E. Marchesi  <jose.marchesi@oracle.com>
	    David Faust <david.faust@oracle.com>

	* bpf-desc.c: Regenerate.
	* bpf-opc.h: Likewise.
	* bpf-opc.c: Likewise.
	* bpf-dis.c: Likewise.