drm/i915/icl: Define Panel power ctrl register

There are two panel power sequencers. Each register
has two addressable instances. This patch defines
both the instances of Panel power control register

Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/99bb687b17a9165527a6210a79271c8175c8a4e3.1543500286.git.jani.nikula@intel.com