staging: bcm2835-codec: Refactor default resolution code

The default resolution code was different for each role
as compressed formats need to pass bytesperline as 0 and
set up customised buffer sizes.
This is common setup, therefore amend get_sizeimage and
get_bytesperline to do the correct thing whether compressed
or uncompressed.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>