Add assembler and disassembler support for the new Armv8.4-a registers for AArch64.

Add assembler and disassembler support for the new Armv8.4-a registers for AArch64.

Some of these instructions have been back-ported as optional extensions to
Armv8.2-a and higher, but others are only available for Armv8.4-a.

opcodes/

	* aarch64-opc.c (aarch64_sys_regs): Add ARMv8.4-a registers;
	dit, vstcr_el2, vsttbr_el2, cnthvs_tval_el2, cnthvs_cval_el2,
	cnthvs_ctl_el2, cnthps_tval_el2, cnthps_cval_el2, cnthps_ctl_el2,
	sder32_el2, vncr_el2.
	(aarch64_sys_reg_supported_p): Likewise.
	(aarch64_pstatefields): Add dit register.
	(aarch64_pstatefield_supported_p): Likewise.
	(aarch64_sys_regs_tlbi): Add vmalle1os, vae1os, aside1os, vaae1os,
	vale1os, vaale1os, ipas2e1os, ipas2le1os, vae2os, vale2os, vmalls12e1os,
	vae3os, vale3os, alle2os, alle1os, alle3os, rvae1, rvaae1, rvale1,
	rvaale1, rvae1is, rvaae1is, rvale1is, rvaale1is, rvae1os, rvaae1os,
	rvale1os, rvaale1os, ripas2e1is, ripas2le1is, ripas2e1, ripas2le1,
	ripas2e1os, ripas2le1os, rvae2, rvale2, rvae2is, rvale2is, rvae2os,
	rvale2os, rvae3, rvale3, rvae3is, rvale3is, rvae3os, rvale3os.

gas/testsuite

	* gas/aarch64/armv8_4-a-registers-illegal.d: New.
	* gas/aarch64/armv8_4-a-registers-illegal.l: New.
	* gas/aarch64/armv8_4-a-registers-illegal.s: New.
	* gas/aarch64/armv8_4-a-registers.d: New.
	* gas/aarch64/armv8_4-a-registers.s: New.