cmd/internal/obj/arm: fix MOVW to/from FPSR

cmd/internal/obj/arm: fix MOVW to/from FPSR

"MOVW FPSR, g" should be assembled to 0xeef1aa10, but actually
0xee30a110 (RFS). "MOVW g, FPSR" should be 0xeee1aa10, but actually
0xee20a110 (WFS). They should be updated to VFP forms, since the ARM
back end doesn't support non-VFP floating points.

The patch fixes them and adds more assembly encoding tests.

fixes #20643

Change-Id: I3b29490337c6e8d891b400fcedc8b0a87b82b527
Reviewed-on: https://go-review.googlesource.com/45276
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>