drm/xe: Avoid doing rebinds

If we dont change page sizes we can avoid doing rebinds rather just do a
partial unbind. The algorithm to determine its page size is greedy as we
assume all pages in the removed VMA are the largest page used in the
VMA.

v2: Don't exceed 100 lines
v3: struct xe_vma_op_unmap remove in different patch, remove XXX comment

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