radeon: Fix KMS CP writeback on big endian machines.

radeon: Fix KMS CP writeback on big endian machines.

BugLink: http://bugs.launchpad.net/bugs/769042

commit dc66b325f161bb651493c7d96ad44876b629cf6a upstream.

This is necessary even with PCI(e) GART, and it makes writeback work even with
AGP on my PowerBook. Might still be unreliable with older revisions of UniNorth
and other AGP bridges though.

Signed-off-by: Michel Dänzer <daenzer@vmware.com>
Reviewed-by: Alex Deucher <alex.deucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Leann Ogasawara <leann.ogasawara@canonical.com>