drm/xe: Restrict huge PTEs to 1GiB

Add a define for the highest level for which we can encode a huge PTE,
and use it for page-table building. Also update an assert that checks that
we don't try to encode for larger sizes.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Brian Welty <brian.welty@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231209151843.7903-2-thomas.hellstrom@linux.intel.com


Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>