drm/xe: Rework xe_exec and the VM rebind worker to use the drm_exec helper

drm/xe: Rework xe_exec and the VM rebind worker to use the drm_exec helper

Replace the calls to ttm_eu_reserve_buffers() by using the drm_exec
helper instead. Also make sure the locking loop covers any calls to
xe_bo_validate() / ttm_bo_validate() so that these function calls may
easily benefit from being called from within an unsealed locking
transaction and may thus perform blocking dma_resv locks in the future.

For the unlock we remove an assert that the vm->rebind_list is empty
when locks are released. Since if the error path is hit with a partly
locked list, that assert may no longer hold true we chose to remove it.

v3:
- Don't accept duplicate bo locks in the rebind worker.
v5:
- Loop over drm_exec objects in reverse when unlocking.
v6:
- We can't keep the WW ticket when retrying validation on OOM. Fix.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230908091716.36984-5-thomas.hellstrom@linux.intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>