Decode AT_PAGESZ to determine physPageSize on netbsd.

Also rename vdso_none.go to auxv_none.go which matches its purpose more
closely.

Akin to CL 99780 which did the same for freebsd.

Change-Id: Iea4322f861ff0f3515e9051585dbb442f024326b
Reviewed-on: https://go-review.googlesource.com/102677
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>