drm/xe: Adjust batchbuffer space warning when creating a job

We should WARN (not BUG) when creating a job if the batchbuffer does not
have sufficient space and padding.  The hardware prefetch requirements
should also be considered.

Link: https://lore.kernel.org/r/20230329173334.4015124-3-matthew.d.roper@intel.com


Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>