[media] v4l2-subdev: replace v4l2_subdev_fh by v4l2_subdev_pad_config

If a subdevice pad op is called from a bridge driver, then there is
no v4l2_subdev_fh struct that can be passed to the subdevice. This
made it hard to use such subdevs from a bridge driver.

This patch replaces the v4l2_subdev_fh pointer by a v4l2_subdev_pad_config
pointer in the pad ops. This allows bridge drivers to use the various
try_ pad ops by creating a v4l2_subdev_pad_config struct and passing it
along to the pad op.

The v4l2_subdev_get_try_* macros had to be changed because of this, so
I also took the opportunity to use the full name of the v4l2_subdev_get_try_*
functions in the __V4L2_SUBDEV_MK_GET_TRY macro arguments: if you now do
'git grep v4l2_subdev_get_try_format' you will actually find the header
where it is defined.

One remark regarding the drivers/staging/media/davinci_vpfe patches: the
*_init_formats() functions assumed that fh could be NULL. However, that's
not true for this driver, it's always set. This is almost certainly a copy
and paste from the omap3isp driver. I've updated the code to reflect the
fact that fh is never NULL.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Tested-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>