cmd/asm: fix the issue of moving 128-bit integers to vector registers on arm64

cmd/asm: fix the issue of moving 128-bit integers to vector registers on arm64

The CL 249758 added `FMOVQ $vcon, Vd` instruction and assembler used
128-bit simd literal-loading to load `$vcon` from pool into 128-bit vector
register `Vd`. Because Go does not have 128-bit integers for now, the
assembler will report an error of `immediate out of range` when
assembleing `FMOVQ $0x123456789abcdef0123456789abcdef, V0` instruction.

This patch lets 128-bit integers take two 64-bit operands, for the high
and low parts separately and adds `VMOVQ $hi, $lo, Vd` instruction to
move `$hi<<64+$lo' into 128-bit register `Vd`.

In addition, this patch renames `FMOVQ/FMOVD/FMOVS` ops to 'VMOVQ/VMOVD/VMOVS'
and uses them to move 128-bit, 64-bit and 32-bit constants into vector
registers, respectively

Update the go doc.

Fixes #40725

Change-Id: Ia3c83bb6463f104d2bee960905053a97299e0a3a
Reviewed-on: https://go-review.googlesource.com/c/go/+/255900
Trust: fannie zhang <Fannie.Zhang@arm.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>