cmd/internal/obj/loong64: add support for instructions F{MAX/NIN}.{S/D}

Go asm syntax:
	F{MAX/MIN}{F/D}		FK, FJ, FD

Equivalent platform assembler syntax:
	f{max/min}.{s/d}	fd, fj, fk

Ref: https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html

Change-Id: Ib11fed1fe3700be5ebba33b5818661c4071b7b7c
Reviewed-on: https://go-review.googlesource.com/c/go/+/590676


Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: abner chenc <chenguoqi@loongson.cn>