drm/i915/kbl: Fix DMC load on Kabylake.

Kabylake A0 is based on Skylake H0.

v2: Don't assume revid+7 and only load the one we are sure about.

v3: Rebase on top of latest changes.

v4: Accept cleaner solution from Jani with kbl_stepping_info
    starting on H0 instead of put a hack on revid.

Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449676319-6959-1-git-send-email-rodrigo.vivi@intel.com