media: rcar-vin: Cache the mbus configuration flags

Media bus configuration flags and media bus type were so far a property
of each VIN instance, as the subdevice they were connected to was
immutable during the whole system life time.

With the forth-coming introduction of parallel input devices support,
a VIN instance can have the subdevice it is connected to switched at
runtime, from a CSI-2 subdevice to a parallel one and viceversa, through
the modification of links between media entities in the media controller
graph. To avoid discarding the per-subdevice configuration flags retrieved by
v4l2_fwnode parsing facilities, cache them in the 'rvin_graph_entity'
member of each VIN instance, opportunely renamed to 'rvin_parallel_entity'.

Also modify the register configuration function to take mbus flags into
account when running on a bus type that supports them.

The media bus type currently in use will be updated in a follow-up patch
to the link state change notification function.

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Acked-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>