gpu: ion: Use standard cache routines

Instead of using custom routines for cache operations use the
standard operations for cache flush, cache clean, and cache
invalidate. In addition only call outer cache routines if
outer cache is available.

Change-Id: Idb51bf7348fd526ebdea1e6ff2e366b8a3b4de33
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>