runtime: start moduledata memory load early

runtime: start moduledata memory load early

The slowest thing that can happen in funcdata is a cache miss
on moduledata.gofunc. Move that memory load earlier.

Also, for better ergonomics when working on this code,
do more calculations as uintptrs.

name                   old time/op  new time/op  delta
StackCopyWithStkobj-8  10.5ms ± 5%   9.9ms ± 4%  -6.03%  (p=0.000 n=15+15)

Change-Id: I590f4449725983c7f8d274c4ac7ed384d9018d85
Reviewed-on: https://go-review.googlesource.com/c/go/+/354134
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>