drm/xe: Simplify locking in new_vma

Rather than acquiring and dropping the VM / BO dma-resv around
xe_vma_create and do the same thing upon adding preempt fences or an
error, hold these locks through the entire new_vma() function.

v2:
 - Rebase (CI)

Cc: Fei Yang <fei.yang@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Jagmeet Randhawa <jagmeet.randhawa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240618003859.3239239-1-matthew.brost@intel.com