[media] mceusb: add support for cx231xx-based IR (e. g. Polaris)

For now, it adds support for Conexant EVK and for Pixelview.
We should probably find a better way to specify all Conexant
Polaris devices, to avoid needing to repeat this setup on
both mceusb and cx231xx-cards.

Reviewed-by: Jarod Wilson <jarod@redhat.com>
Acked-by: Sri Devi <Srinivasa.Deevi@conexant.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>