V4L/DVB (11790): xc5000: restore sleep routine

Bring back the code that puts the xc5000 to sleep.  For the Pinnacle 801e
this results in power consumption at idle dropping from 325ma to 124ma.

If there are *actually* any devices that don't work in this configuration,
they should set dvb_frontend.ops.tuner_ops.sleep to NULL (per mkrufky's
suggestion)

Also, had to make sure we were making sure the firmware was loaded in the
digital version of set_params, or else we end up get i2c errors if the
device is asleep

Signed-off-by: Devin Heitmueller <devin.heitmueller@gmail.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>