cmd/internal/obj/arm64: pass obj.As to oaddi rather than an instruction
This simplifies callers, as they do not need to call opirr before calling oaddi.
Additionally, use appropriate types (int16) for registers, which avoids the need
to continually cast.
Change-Id: I8ca3807a97867ac49d63792f6922a18f35824448
Reviewed-on: https://go-review.googlesource.com/c/go/+/471520 Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Joel Sing <joel@sing.id.au> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>