[media] bcm2048: add TODO file for this staging driver

Describe the tasks to be done for this driver to be promoted to a
non-staging one.

[m.chehab@samsung.com: Add a patch description; add a note about the
 CodingStyle issues and make sure that the README lines are not bigger
 than 80 cols.]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>