drm/xe: Fix potential integer overflow in page size calculation

Explicitly cast tbo->page_alignment to u64 before bit-shifting to
prevent overflow when assigning to min_page_size.

Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240318164342.3094-1-nirmoy.das@intel.com