This patch adds support to the ADV7180 driver to check the input
status.

Since the status is held in the same register as the input standard
a small restructuring of the code is done to reuse the code for
reading the register
Signed-off-by: Richard Röjfors <richard.rojfors@mocean-labs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>