[media] marvell-cam: Separate out the Marvell camera core

There will eventually be multiple users of the core camera controller, so
separate it from the bus/platform/i2c stuff.  I've tried to do the minimal
set of changes to get the driver functioning in this configuration; I did
clean up a bunch of old checkpatch gripes in the process.  This driver
works like the old one did on OLPC XO 1 systems.

Cc: Daniel Drake <dsd@laptop.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>