media: si2157: Add analog tuning related functions

Include set_analog_params, get_frequency, and get_bandwidth.

Tested with NTSC and PAL standards via ch3/4 generator. Other standards
are included, but are untested due to lack of generator.

Signed-off-by: Brad Love <brad@nextdimension.cc>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>