cmd/internal/obj, cmd/asm: reclassify 32-bit immediate value of loong64

cmd/internal/obj, cmd/asm: reclassify 32-bit immediate value of loong64

Change-Id: If9fd257ca0837a8c8597889c4f5ed3d4edc602c1
Reviewed-on: https://go-review.googlesource.com/c/go/+/636995
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>