V4L/DVB (11798): xc5000: add "no_poweroff" module option

Provide for the ability for a user to disable putting the tuner to sleep, in
case he doesn't want to incur the cost of reloading the firmware when starting
up his/her application.  The module options are intentionally identical to
xc3028.

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>