cmd/link: move all FUNCDATA refs into go.func.*

cmd/link: move all FUNCDATA refs into go.func.*

This change moves all symbols referred to by FUNCDATA
into go.func.* and go.funcrel.*.

Surprisingly (because it inhibits some content-addressability),
it shrinks binaries by a little bit, about 0.1%.

This paves the way for a subsequent change to change
FUNCDATA relocations to offsets.

Change-Id: I70e487205073699f442192b0791cc92da5663057
Reviewed-on: https://go-review.googlesource.com/c/go/+/352189
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>