xtensa: cache inquiry and unaligned cache handling functions

The existing xtensa cache handling functions work on page-aligned
memory regions.

These functions are needed for the s6000 dma engine which can work on
a byte-granularity.

Signed-off-by: Oskar Schirmer <os@emlix.com>
Cc: Johannes Weiner <jw@emlix.com>
Cc: Daniel Glockner <dg@emlix.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Zankel <chris@zankel.net>