media: renesas: vsp1: Compute partitions for DRM pipelines

media: renesas: vsp1: Compute partitions for DRM pipelines

The DRM pipelines don't partition frames, as the hardware operates
synchronously with the display. The entity operations access
configuration data from the entity state in that case, instead of
accessing the partition structure. This requires special cases in
entity-specific code, increasing the driver complexity.

To prepare for simplifying the code, initialize a single partition for
the DRM pipelines, similarly to how video pipelines create one partition
spanning the full image when partitioning isn't needed. The partition is
allocated statically in the vsp1_drm_pipeline structure instead of
dynamically as for video pipelines, as DRM pipelines are guaranteed to
operate on a single partition.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi+renesas@ideasonboard.com>