media: tvp5150: convert register access to regmap

Regmap provides built in debugging, caching and provides dedicated
accessors for bit manipulations in registers, which make the following
changes a lot simpler.
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>