V4L/DVB (12864): tda18271: change output feature configuration to a bitmask

For better readability, treat the low power standby mode configuration
as an output option feature configuration, and change it to a bitmask.

If left unconfigured, all features will remain enabled, just as the
default configuration was before these changes were introduced.

Signed-off-by: Michael Krufky <mkrufky@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>