media: camss: Add missing format identifiers

The CSI-2 spec defines format identifier for Data Type (DT),
and how the Decode Format (DF) & Encode Format (EF) are implemented.
The spec does however not define the DF, EF or Plain Format (PF)
identifiers, as those are vendor specific.

Plain formats describe the size of the pixels written by the RDI
units to memory. PLAIN8 for example has the size 8 bits, and
PLAIN32 32 bits. The appropriate Plain Format is determined by
the Decode Format used. The smallest Plain Format that is able
to contain a pixel of the used Decode Format is the appropriate
one to use.

As the vendor specific identifiers differ between hardware
generations, split them out into separate headers.

Signed-off-by: Robert Foss <robert.foss@linaro.org>
Reviewed-by: Andrey Konovalov <andrey.konovalov@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>