[Morello] Add capability register set support

[Morello] Add capability register set support

This patch adds capability register set support to both GDB and GDBserver,
allowing the use of ptrace.

gdb/ChangeLog

2020-10-20  Luis Machado  <luis.machado@arm.com>

	* aarch64-linux-nat.c: Include arch/aarch64-cap-linux.h.
	(fetch_cregs_from_thread)
	(store_cregs_to_thread): New functions.
	(aarch64_linux_nat_target::fetch_registers): Modify to check for
	capability registers.
	* aarch64-linux-tdep.c: Include arch/aarch64-cap-linux.h.
	* aarch64-tdep.c (aarch64_cannot_store_register): Check for capability
	registers.
	(aarch64_gdbarch_init): Also save the last capability register number.
	* aarch64-tdep.h (struct gdbarch_tdep) <cap_reg_last>: New field.
	* arch/aarch64-cap-linux.h (AARCH64_LINUX_CREGS_SIZE,
	AARCH64_MORELLO_REGS_NUM, AARCH64_C_REGS_NUM): New constants.
	* arch/aarch64.c: Remove FIXME comment.
	* nat/aarch64-linux.h (user_morello_state): New struct.

gdbserver/ChangeLog

2020-10-20  Luis Machado  <luis.machado@arm.com>

	* linux-aarch64-low.c: arch/aarch64-cap-linux.h.
	(aarch64_store_cregset): New function.
	(aarch64_regsets): Add capability register set.
	(aarch64_sve_regsets): Likewise.

include/ChangeLog

2020-10-20  Luis Machado  <luis.machado@arm.com>

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