Multi-planar planes can be imported from VA-API or V4L2. In this case we
would currently report wrong values for `gbm_bo_get_offset()`.
This does not fix any know visible bug, as crocus hardware usually does
not support muliti-planar planes in the display engine - in which case
the wrong values would make Mutter glitch. Lets report correct values
regardless.
While on it, also use the helper function for counting planes.
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28225>
Robert Mader
b2719a73c1