[media] media: Add new SDR formats PC16, PC18 & PC20

This patch adds support for the three new SDR formats. These formats
were prefixed with "planar" indicating I & Q data are not interleaved
as in other formats. Here, I & Q data constitutes the top half and bottom
half of the received buffer respectively.

V4L2_SDR_FMT_PCU16BE - 14-bit complex (I & Q) unsigned big-endian sample
inside 16-bit. V4L2 FourCC: PC16

V4L2_SDR_FMT_PCU18BE - 16-bit complex (I & Q) unsigned big-endian sample
inside 18-bit. V4L2 FourCC: PC18

V4L2_SDR_FMT_PCU20BE - 18-bit complex (I & Q) unsigned big-endian sample
inside 20-bit. V4L2 FourCC: PC20

Signed-off-by: Ramesh Shanmugasundaram <ramesh.shanmugasundaram@bp.renesas.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>