drm/msm: cache maintenance update for ion dmabuf

ION dmabuf handling has changed the way dma_buf_map_attachment is
used. Cache maintenance will be invoked during dma_buf_map_attachment
and it is necessary to move this call from gem_prime_import to
msm_framebuffer_prepare for uncached buffers. All the attachment
attribute settings need to be provided during the
dma_buf_map_attachment time.

Change-Id: Ie7118f72a7c4cd6faaf2b5ceec4b570888342241
Signed-off-by: Benjamin Chan <bkchan@codeaurora.org>
Signed-off-by: Steve Cohen <cohens@codeaurora.org>