cmd/internal/obj/arm64: Add helpers for span7 passes
Adds helper functions for the literal pooling, large branch handling
and code emission stages of the span7 assembler pass. This hides the
implementation of the current assembler from the general workflow in
span7 to make the implementation easier to change in future.
Updates #44734
Change-Id: I8859956b23ad4faebeeff6df28051b098ef90fed
Reviewed-on: https://go-review.googlesource.com/c/go/+/595755 Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>