AArch64: Add MTE register set support for GDB and gdbserver

AArch64: Add MTE register set support for GDB and gdbserver

AArch64 MTE support in the Linux kernel exposes a new register
through ptrace.  This patch adds the required code to support it.

include/ChangeLog:

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

	* elf/common.h (NT_ARM_TAGGED_ADDR_CTRL): Define.

gdb/ChangeLog:

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

	* aarch64-linux-nat.c (fetch_mteregs_from_thread): New function.
	(store_mteregs_to_thread): New function.
	(aarch64_linux_nat_target::fetch_registers): Update to call
	fetch_mteregs_from_thread.
	(aarch64_linux_nat_target::store_registers): Update to call
	store_mteregs_to_thread.
	* aarch64-tdep.c (aarch64_mte_register_names): New struct.
	(aarch64_cannot_store_register): Handle MTE registers.
	(aarch64_gdbarch_init): Initialize and setup MTE registers.
	* aarch64-tdep.h (gdbarch_tdep) <mte_reg_base>: New field.
	<has_mte>: New method.
	* arch/aarch64-linux.h (AARCH64_LINUX_SIZEOF_MTE): Define.

gdbserver/ChangeLog:

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

	* linux-aarch64-low.cc (aarch64_fill_mteregset): New function.
	(aarch64_store_mteregset): New function.
	(aarch64_regsets): Add MTE register set entry.
	(aarch64_sve_regsets): Add MTE register set entry.