Eliminate an unused macro whose name clashes now with a function in the
new cpu-v6.h.  This should have been part of r276334.
Add cache maintenance functions which will be used by startup code to
initially set up the MMU.  Some day they may also be useful as part of
suspend/resume handling, when we get better at power management.

Submitted by: Svatopluk Kraus <onwahe@gmail.com>,
              Michal Meloun <meloun@miracle.cz