arm: move unrolled loops back to generic code

arm: move unrolled loops back to generic code

Some of the ARM functions differed from their generic counterparts
only by unrolling their loops. Since this change may be useful
on other platforms, or might even supercede the looped version
in the generic case, move it back to the generic file.

This code is left under #if ARCH_ARM for now, but it may be worth
considering a different (possibly new) conditional for these. If
it turns out that this should be runtime selectable, these
functions will have to move to the RTCD infrastructure. Don't want
to take that step at this time without more profile data.

Change-Id: I4612fdbc606fbebba4971a690fb743ad184ff15f