drm/i915/gvt: Add new 64K entry type

Add a new entry type GTT_TYPE_PPGTT_PTE_64K_ENTRY. 64K entry is very
different from 2M/1G entry. 64K entry is controlled by IPS bit in upper
PDE. To leverage the current logic, I take IPS bit as 'PSE' for PTE
level. Which means, 64K entries can also processed by get_pse_type().

v2: Make it bisectable.

Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>