ARM: outer cache: add documentation of outer cache functions
ARM: outer cache: add documentation of outer cache functions

Add some documentation to cover the outer cache functions so that their
requirements can be better understood.  Of particular note are the
flush_all() and disable() methods which must not be called except in
very specific circumstances.

Signed-off-by: Russell King <f6aa0246ff943bfa8602cdf60d40c481b38ed232@arm.linux.org.uk>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs