[media] V4L: soc-camera: avoid huge arrays, caused by changed format codes

Recently mediabus pixel format codes have become a part of the user-
space API, at which time their values also have been changed from
contiguous numbers, running from 0 to sparse numbers with values
around 0x1000, 0x2000, 0x3000... This made them unsuitable for the
use as array indices. This patch switches soc-camera internal format
look-ups to not depend on values of those macros.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>