media: vimc: Make capture devices and subdevices use different link_validates

Instead of validating the links to capture devices and subdevices with
the same function, use the default v4l function for links between
subdevices and only use a different function for validating between
capture device and subdevice.
This change should also ease future work to associate multiple mbus
codes for the same pixelformat in vimc_pix_map.

These changes were tested with
v4l2-compliance SHA: 3f806630e2ecbcebe31872b865c5c4b42f111a99, 64 bits
and passed all tests:
Grand Total for vimc device /dev/media0: 451, Succeeded: 451, Failed: 0, Warnings: 0

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@protonmail.com>
Acked-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>