drm/omap: Add a 'right overlay' to plane state

If the drm_plane has a source width that's greater than the max width
supported by a single hw overlay, then we assign a 'r_overlay' to it in
omap_plane_atomic_check().

Both overlays should have the capabilities required to handle the source
framebuffer. The only parameters that vary between the left and right
hwoverlays are the src_w, crtc_w, src_x and crtc_x as we just even chop
the fb into left and right halves.

We also take care of not creating odd width size when dealing with YUV
formats.

Since both halves need to be 'appear' side by side the zpos is
recalculated when dealing with dual overlay cases so that the other
planes zpos is consistent.

Depending on user space usage it is possible that on occasion the number
of requested planes exceeds the numbers of overlays required to display
them. In that case a failure would be returned for the plane that cannot
be handled at that time. It is up to user space to make sure the H/W
resource are not over-subscribed.

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211117141928.771082-10-narmstrong@baylibre.com