HDMI register offsets are different in Valleyview. Add support for the
same.

v2: drop superfluous comments in HDMI init (Daniel)
Signed-off-by: NBeeresh G <beeresh.g@intel.com>
Signed-off-by: NShobhit Kumar <shobhit.kumar@intel.com>
Reviewed-by: NVijay Purushothaman <vijay.a.purushothaman@intel.com>
Reviewed-by: NJesse Barnes <jesse.barnes@intel.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>