drm/xe/migrate: Update emit_pte to cope with a size level than 4k

emit_pte assumes the size argument is 4k aligned, this may not be true
for the PTEs emitted for CSS as seen by below call stack:

[   56.734228] xe_migrate_copy:585: size=327680, ccs_start=327680, css_size=1280,4096
[   56.734250] xe_migrate_copy:643: size=262144
[   56.734252] emit_pte:404: ptes=64
[   56.734255] emit_pte:418: chunk=64
[   56.734257] xe_migrate_copy:650: size=1024	@ CCS emit PTE
[   56.734259] emit_pte:404: ptes=1
[   56.734261] emit_pte:418: chunk=1
[   56.734339] xe_migrate_copy:643: size=65536
[   56.734342] emit_pte:404: ptes=16
[   56.734344] emit_pte:418: chunk=16
[   56.734346] xe_migrate_copy:650: size=256	# CCS emit PTE
[   56.734348] emit_pte:404: ptes=1
[   56.734350] emit_pte:418: chunk=1
[   56.734352] xe_res_next:174: size=4096, remaining=0

Update emit_pte to handle sizes less than 4k.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>