bpf: xBPF SDIV, SMOD instructions

bpf: xBPF SDIV, SMOD instructions

Add gas and opcodes support for two xBPF-exclusive ALU operations:
SDIV (signed division) and SMOD (signed modulo), and add tests for
them in gas.

cpu/
	* bpf.cpu (insn-op-code-alu): Add SDIV and SMOD.
	(define-alu-insn-bin, daib): Take ISAs as an argument.
	(define-alu-instructions): Update calls to daib pmacro with
	ISAs; add sdiv and smod.

gas/
	* testsuite/gas/bpf/alu-xbpf.d: New file.
	* testsuite/gas/bpf/alu-xbpf.s: Likewise.
	* testsuite/gas/bpf/alu32-xbpf.d: Likewise.
	* testsuite/gas/bpf/alu32-xbpf.d: Likewise.
	* testuiste/gas/bpf/bpf.exp: Run new tests.

opcodes/
	* bpf-desc.c: Regenerate.
	* bpf-desc.h: Likewise.
	* bpf-opc.c: Likewise.
	* bpf-opc.h: Likewise.