cmd/internal/obj, cmd/asm: reclassify the offset of memory access operations on loong64

cmd/internal/obj, cmd/asm: reclassify the offset of memory access operations on loong64

This CL also fixes the encoding error of LL/SC[V] instruction and
adds the handling of offset greater than 16 bits in MOV{W/V}P instructions.

Change-Id: I7a8fab4b68a6839da81c5e59af1f42289d00ef61
Reviewed-on: https://go-review.googlesource.com/c/go/+/706435
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Meidan Li <limeidan@loongson.cn>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Michael Knyszek <mknyszek@google.com>