V4L/DVB (7003): cx23885: Add support for device revision detection

Each version of the cx23885/7/8 silicon has different build revs.
We'll use this internal revision to work around bugs and known
issues in the video and encoder related patches.

Signed-off-by: Steven Toth <stoth@hauppauge.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>