drm/xe/migrate: rework size restrictions for sram pte emit

drm/xe/migrate: rework size restrictions for sram pte emit

We allow the input size to not be aligned to PAGE_SIZE, which leads to
various bugs in build_pt_update_batch_sram() for PAGE_SIZE > 4K systems.
For example if ptes is exactly one gpu_page_size then the chunk size is
rounded down to zero.  The simplest fix looks to be forcing PAGE_SIZE
aligned inputs.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20251022163836.191405-3-matthew.auld@intel.com