AArch64: Implement the memory tagging gdbarch hooks

AArch64: Implement the memory tagging gdbarch hooks

This patch implements the memory tagging gdbarch hooks for AArch64, for
the MTE feature.

gdb/ChangeLog:

2021-03-24  Luis Machado  <luis.machado@linaro.org>

	* aarch64-linux-tdep.c: Include target.h, arch-utils.h, value.h.
	(aarch64_mte_get_atag, aarch64_linux_tagged_address_p)
	(aarch64_linux_memtag_mismatch_p, aarch64_linux_set_memtags)
	(aarch64_linux_get_memtag, aarch64_linux_memtag_to_string): New
	functions.
	(aarch64_linux_init_abi): Initialize MTE-related gdbarch hooks.
	* arch/aarch64-mte-linux.c (aarch64_mte_make_ltag_bits)
	(aarch64_mte_make_ltag, aarch64_linux_set_ltag)
	(aarch64_linux_get_ltag): New functions.
	* arch/aarch64-mte-linux.h (AARCH64_MTE_LOGICAL_TAG_START_BIT)
	(AARCH64_MTE_LOGICAL_MAX_VALUE): Define.
	(aarch64_mte_make_ltag_bits, aarch64_mte_make_ltag)
	(aarch64_mte_set_ltag, aarch64_mte_get_ltag): New prototypes.