[media] mn88473: add DVB-T2 PLP support

Adds PLP ID filtering for DVB-T2.

It is untested as I don't have any signal having PLP ID other than 0.
There is only 2 extra registers, 0x32 and 0x36 on bank2, that are
programmed for DVB-T2 but not for DVB-T and all the rest are
programmed similarly - so it is likely PLP.

Pridvorov reported successfully testing it in Russia with m-PLP streams,
on both Vladivostok and Moskow.

Tested-by: "Придворов Андрей (Pridvorov Andrey)" <ua0lnj@bk.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>