On ARM, DIV, DIVU, MOD, MODU are pseudo instructions that makes
runtime calls _div/_udiv/_mod/_umod, which themselves are wrappers
of udiv. The udiv function does the real thing.

Instead of generating these pseudo instructions, call to udiv
directly. This removes one layer of wrappers (which has an awkward
way of passing argument), and also allows combining DIV and MOD
if both results are needed.

Change-Id: I118afc3986db3a1daabb5c1e6e57430888c91817
Reviewed-on: https://go-review.googlesource.com/29390Reviewed-by: David Chase <drchase@google.com>