Hi

This patch adds the new LDGM/STGM instructions of the
Armv8.5-A Memory Tagging Extension. This is part of the changes
that have been introduced recently in the 00bet10 release
https://developer.arm.com/architectures/cpu-architecture/a-profile/exploration-tools

The instructions are as follows:
LDGM Xt, [<Xn|SP>]
https://developer.arm.com/docs/ddi0596/latest/base-instructions-alphabetic-order/ldgm-load-tag-multiple

STGM Xt, [<Xn|SP>]
https://developer.arm.com/docs/ddi0596/latest/base-instructions-alphabetic-order/stgm-store-tag-multiple

For ease of review I have not added the regenerated files in the patch. 
I will add those in my final commit.

Builds and reg tests all pass on aarch64-none-elf.

Is this ok for trunk? And for backport to 2.32?

Thanks
Sudi

*** gas/ChangeLog ***

2019-xx-xx  Sudakshina Das  <sudi.das@arm.com>

	* testsuite/gas/aarch64/armv8_5-a-memtag.d: New tests for ldgm and stgm.
	* testsuite/gas/aarch64/armv8_5-a-memtag.s: Likewise.
	* testsuite/gas/aarch64/illegal-memtag.l: Likewise.
	* testsuite/gas/aarch64/illegal-memtag.s: Likewise.

*** opcodes/ChangeLog ***

2019-xx-xx  Sudakshina Das  <sudi.das@arm.com>

	* aarch64-asm-2.c: Regenerated.
	* aarch64-dis-2.c: Likewise.
	* aarch64-opc-2.c: Likewise.
	* aarch64-tbl.h (aarch64_opcode): Add new ldgm and stgm.