cmd/asm: rename arm64 instructions LDANDx to LDCLRx

cmd/asm: rename arm64 instructions LDANDx to LDCLRx

The LDANDx instructions were misleading because they correspond to the
mnemonic LDCLRx as defined in the Arm Architecture Reference Manual for
Armv8. This changes the assembler to use the same mnemonic as the GNU
assembler and the manual.

The instruction has the form:

LDCLRx Rs, (Rb), Rt: *Rb -> Rt, Rs AND NOT(*Rb) -> *Rb

Change-Id: I94ae003e99e817209bba1afe960e612bf3a0b410
Reviewed-on: https://go-review.googlesource.com/c/go/+/267138
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: fannie zhang <Fannie.Zhang@arm.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: fannie zhang <Fannie.Zhang@arm.com>