AArch64: Add pauth DWARF registers

AArch64: Add pauth DWARF registers

Map the pauth registers to DWARF.

Add a new pseudo register ra_state and also map this to DWARF.  This register
is hidden from the user - prevent it from being read or written to.  It will
be used for the unmangling of addresses.

gdb/ChangeLog:

	* aarch64-tdep.c (aarch64_dwarf_reg_to_regnum): Check for pauth
	registers.
	(aarch64_pseudo_register_name): Likewise.
	(aarch64_pseudo_register_type): Likewise.
	(aarch64_pseudo_register_reggroup_p): Likewise.
	(aarch64_gdbarch_init): Add pauth registers.
	* aarch64-tdep.h (AARCH64_DWARF_PAUTH_RA_STATE): New define.
	(AARCH64_DWARF_PAUTH_DMASK): Likewise.
	(AARCH64_DWARF_PAUTH_CMASK): Likewise.
	(struct gdbarch_tdep): Add regnum for ra_state.