media: am437x-vpfe: TRY_FMT ioctl is not really trying anything

The try_fmt was not actually trying out the provided format
but merely returning the current format basically like get_fmt.
In addition set_fmt should first invoked try_fmt to validate the
given format before applying it to the hardware.

To fix all of these the whole get/try/set ioctl functions had to
be reworked.
When calculating the bytesperline/stride and sizeimage format
member we don't need to locally store the current value of
bytesperpixel as it can easily get derived dynamically.

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Acked-by: Lad Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>