Remove the ARM_USE_SMALL_ALLOC option and code related to it.

This was an optimization used only by a few xscale platforms.  Part of
the optimization was to create a direct map for all physical pages, and
that resulted in making multiple mappings of pages in a way that bypassed
the logic in pmap.c to handle VIVT cache aliasing.  It also just generally
made the code more complex and hard to maintain for all SoCs.

Reviewed by:	cognet