aarch64: Add LSE128 instructions

Implement, together with the necessary tests, the following new LSE128
atomic instructions:

  * Atomic bit clear on quadword in memory (ldclrp{a|l|al});
  * Atomic bit set on quadword in memory (ldsetp{a|l|al});
  * Swap quadword in memory (swpp{a|l|al});

gas/ChangeLog:

	* testsuite/gas/aarch64/lse128-atomic.d: New.
	* testsuite/gas/aarch64/lse128-atomic.s: Likewise.

opcodes/ChangeLog:

	* aarch64-tbl.h (ldclrp): new _LSE128_INSN entry.
	(ldclrpa):  Likewise.
	(ldclrpal): Likewise.
	(ldclrpl): Likewise.
	(ldsetp): Likewise.
	(ldsetpa): Likewise.
	(ldsetpal): Likewise.
	(ldsetpl): Likewise.
	(swpp): Likewise.
	(swppa): Likewise.
	(swppal): Likewise.
	(swppl): Likewise.
	* aarch64-asm-2.c: Regenerate.
	* aarch64-dis-2.c: Likewise.
	* aarch64-opc-2.c: Likewise.