AArch64: Add pauth core file section

AArch64: Add pauth core file section

Used for the AArch64 pointer authentication code mask registers in Arm v8.3-a.

NT_ARM_PAC_MASK matches the value in Linux include/uapi/linux/elf.h

include/ChangeLog:

	* elf/common.h (NT_ARM_PAC_MASK): Add define.

bfd/ChangeLog:

	* elf-bfd.h (elfcore_write_aarch_pauth): Add declaration.
	* elf.c (elfcore_grok_aarch_pauth): New function.
	(elfcore_grok_note): Check for NT_ARM_PAC_MASK.
	(elfcore_write_aarch_pauth): New function.
	(elfcore_write_register_note): Check for AArch64 pauth section.