drm/xe/fbdev: use the same 64-byte stride alignment as i915

drm/xe/fbdev: use the same 64-byte stride alignment as i915

For reasons unknown, xe uses XE_PAGE_SIZE alignment for
stride. Presumably it's just a confusion between stride alignment and bo
allocation size alignment. Switch to 64 byte alignment to, uh, align
with i915.

This will also be helpful in deduplicating and unifying the xe and i915
framebuffer allocation.

Link: https://lore.kernel.org/r/aLqsC87Ol_zCXOkN@intel.com
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/7f4972104de8b179d5724ae83892ee294d3f3fd3.1758184771.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>