drm/panfrost: Use xarray and helpers for depedency tracking

More consistency and prep work for the next patch.

Aside: I wonder whether we shouldn't just move this entire xarray
business into the scheduler so that not everyone has to reinvent the
same wheels. Cc'ing some scheduler people for this too.

v2: Correctly handle sched_lock since Lucas pointed out it's needed.

v3: Rebase, dma_resv_get_excl_unlocked got renamed

v4: Don't leak job references on failure (Steven).

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Luben Tuikov <luben.tuikov@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210622165511.3169559-6-daniel.vetter@ffwll.ch