drm/i915/skl: Sunrise Point PCH detection

This patch implements detection of SPT and SPT-LP PCH devices.

v2: Added HAS_PCH_SPT macro

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Satheeshakrishna M <satheeshakrishna.m@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>