[media] xc4000: setting registers

This patch implements setting the registers in xc4000_set_params()
and xc4000_set_analog_params(). A new register is defined which enables
filtering of the composite video output (this is needed to avoid bad
picture quality with some boards).

Signed-off-by: Istvan Varga <istvan_v@mailbox.hu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>