arm: prop up software floating point

arm: prop up software floating point

Just enough to make mov instructions work,
which in turn is enough to make strconv work
when it avoids any floating point calculations.
That makes a bunch of other packages pass
their tests.

Should suffice until hardware floating point
is available.

Enable package tests that now pass
(some due to earlier fixes).

Looks like there is a new integer math bug
exposed in the fmt and json tests.

R=ken2
CC=golang-dev
https://golang.org/cl/2638041