Decode AT_PAGESZ to determine physPageSize on freebsd/{386,amd64,arm}
and AT_HWCAP for hwcap and hardDiv on freebsd/arm. Also use hwcap to
perform the FP checks in checkgoarm akin to the linux/arm
implementation.

Change-Id: I532810a1581efe66277e4305cb234acdc79ee91e
Reviewed-on: https://go-review.googlesource.com/99780
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>