dib7000p/dib8000: added pid filtering

dib8000: the SNR is in 10th of dB (not in dB)
dib7000p and dib8000: added the pid filtering. This feature is enabled by module option (dvb-usb module).
Signed-off-by: NOlivier Grenie <olivier.grenie@dibcom.fr>
Signed-off-by: NPatrick Boettcher <pboettcher@kernellabs.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>