[media] marvell-cam: Make suspend/resume work on MMP2

Somehow I didn't ever quite get around to implementing suspend/resume on
the MMP2 platform; this patch fixes that little oversight.  A bit of core
work was necessary to do the right thing in the s/g DMA case.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>