drm/i915: Pass VLV_DISPLAY_BASE + reg to intel_{hdmi, dp}_init on VLV

When passing the DP/HDMI/SDVO registers to the encoder init functions,
include the VLV specific offset in the value.

v2: Resolved conflicts w/ VLV SDVO elimination

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>