[media] xc5000: add IF output level control

Adds control of the IF output level to the xc5000 tuner
configuration structure.  Increases the IF level to the
demodulator to fix failure to lock and picture breakup
issues (with the au8522 demodulator, in the case of the
Hauppauge HVR950Q).

This patch works with all XC5000 firmware versions.

Signed-off-by: Richard Vollkommer <linux@hauppauge.com>
Signed-off-by: Michael Ira Krufky <mkrufky@linuxtv.org>
Reviewed-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>