cmd/link: access pcdata via aux symbols

cmd/link: access pcdata via aux symbols

Pcdata are now separate aux symbols. Read them from aux, instead
of using funcinfo.

Now we can remove pcdata fields from funcinfo.

Change-Id: Ie65e3962edecc0f39127a5f6963dc59d1f141e67
Reviewed-on: https://go-review.googlesource.com/c/go/+/352893
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>