drm/i915/icp: Introduce Ice Lake PCH

Add the enum additions to ICP PCH.

v2 (from Paulo): don't set any platforms to it yet since ICP support is
incomplete.
v3 (from Rodrigo): Fix ICP name.

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180111180010.24357-4-paulo.r.zanoni@intel.com