cmd/internal/obj/loong64: add {,X}VSHUF.{B/H/W/V} instructions support

cmd/internal/obj/loong64: add {,X}VSHUF.{B/H/W/V} instructions support

Go asm syntax:
         VSHUFB             V1, V2, V3, V4
        XVSHUFB             X1, X2, X3, X4
         VSHUF{H/W/V}       V1, V2, V3
        XVSHUF{H/W/V}       X1, X2, X3

Equivalent platform assembler syntax:
         vshuf.b            v4, v3, v2, v1
        xvshuf.b            x4, x3, x2, x1
         vshuf.{h/w/d}      v3, v2, v1
        xvshuf.{h/w/d}      x3, x2, x1

Change-Id: I8983467495f587cf46083fd81cb024400c7dc2a7
Reviewed-on: https://go-review.googlesource.com/c/go/+/716804
Reviewed-by: Meidan Li <limeidan@loongson.cn>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn>