drm/xe/migrate: Fix and clarify some size calculations

We were using the curs->remaining rather than the curs->size field to calculate the remaing size of the current vram segment. That might blow up if the bo vram allocation is fragmented. Fix that.

Also update the batch buffer calculation slightly to limit the blit size earlier and presuming that the batch buffer size calculation is now correct and the workaround for issue #52 (closed) is no longer needed.

Prefix with Draft: since not yet properly tested on anything but DG1.

Signed-off-by: Thomas Hellström thomas.hellstrom@linux.intel.com