Deblocking filter allows to reduce blocking artifacts and improve
visual quality. This is configurable via the V4L2 API but eventually
not applied to the encoder.

Note that alpha and beta deblocking values are 32-bit signed (-6;+6).
Signed-off-by: NLoic Poulain <loic.poulain@linaro.org>
Reviewed-by: NStanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>