drm/i915: VLV2 - Fix hotplug detect bits

Add new definitions for hotplug live status bits for VLV2 since they're
in reverse order from the gen4x ones.

Changelog:
- Restored gen4 bit definitions
- Added new definitions for VLV2
- Added platform check for IS_VALLEYVIEW() in dp_detect to use the correct
  bit defintions
- Replaced a lost trailing brace for the added switch()

Signed-off-by: Todd Previte <tprevite@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=73951
[danvet: Switch to _VLV postfix instead of prefix and regroupg
comments again so that the g4x warning is right next to those defines.
Also add a _G4X suffix for those special ones. Also cc stable.]
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>