Configurations like virtualized environments may support only 48 bit
ppGTT without supporting 32 bit ppGTT. Support this by disconnecting
the relationship of the two feature bits.

Cc: Tina Zhang <tina.zhang@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>