drm/i915/mtl: MMIO range is now 4MB

Previously only dgfx platforms had a 4MB MMIO range, but starting with
MTL we now use the larger range for all platforms.

Bspec: 63834, 63830
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Reviewed-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220818234202.451742-4-radhakrishna.sripada@intel.com