aarch64: Implement 128-bit extension to ACLE sysreg r/w builtins

aarch64: Implement 128-bit extension to ACLE sysreg r/w builtins

Implement the ACLE builtins for 128-bit system register manipulation:

  * __uint128_t __arm_rsr128(const char *special_register);
  * void __arm_wsr128(const char *special_register, __uint128_t value);

gcc/ChangeLog:

	* config/aarch64/aarch64-builtins.cc (AARCH64_RSR128): New
	`enum aarch64_builtins' value.
	(AARCH64_WSR128): Likewise.
	(aarch64_init_rwsr_builtins): Init `__builtin_aarch64_rsr128'
	and `__builtin_aarch64_wsr128' builtins.
	(aarch64_expand_rwsr_builtin): Extend function to handle
	`__builtin_aarch64_{rsr|wsr}128'.
	* config/aarch64/aarch64-protos.h (aarch64_retrieve_sysreg):
	Update function signature.
	* config/aarch64/aarch64.cc (F_REG_128): New.
	(aarch64_retrieve_sysreg): Add 128-bit register mode check.
	* config/aarch64/aarch64.md (UNSPEC_SYSREG_RTI): New.
	(UNSPEC_SYSREG_WTI): Likewise.
	(aarch64_read_sysregti): Likewise.
	(aarch64_write_sysregti): Likewise.
	* config/aarch64/arm_acle.h (__arm_rsr128): New.
	(__arm_wsr128): Likewise.