cmd/internal/obj/loong64: add {V,XV}{FSQRT/FRECIP/FRSQRT}.{S/D} instructions support

cmd/internal/obj/loong64: add {V,XV}{FSQRT/FRECIP/FRSQRT}.{S/D} instructions support

Go asm syntax:
	 V{FSQRT/FRECIP/FRSQRT}{F/D}	VJ, VD
	XV{FSQRT/FRECIP/FRSQRT}{F/D}	XJ, XD

Equivalent platform assembler syntax:
	 v{fsqrt/frecip/frsqrt}.{s/d}	vd, vj
	xv{fsqrt/frecip/frsqrt}.{s/d}	xd, xj

Change-Id: I3fdbe3193659d7532164451b087ccf725053172f
Reviewed-on: https://go-review.googlesource.com/c/go/+/636395
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>