MAINTAINERS: drm/sched: Add new maintainers

DRM's GPU scheduler is arguably in need of more intensive maintenance.
Danilo and Philipp volunteer to help with the maintainership.

Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Luben Tuikov <ltuikov89@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Matthew Brost <matthew.brost@intel.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240916185159.35727-3-pstanner@redhat.com