(pre-stable) drm/i915: make sure eDP panel is turned on

BugLink: http://bugs.launchpad.net/bugs/578673

Small modifications needed because of avariable rename.

When enabling the eDP port, we need to make sure the panel is turned on
after training the link.  If we don't, it likely won't come back after
suspend or may not come up at all.

For unknown reasons, unlocking the panel regs before initiating a power
on sequence is necessary.  There are known bugs in the PCH panel
sequencing logic, apparently this is one possible workaround.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=28739.

OriginalAuthor: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: "Paulo J. S. Silva" <pjssilva@gmail.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
(backported from commit c9fcc5d269949a0fbd46ffbea6cc83741e61c05f upstream)
Acked-by: Brad Figg <brad.figg@canonical.com>
Acked-by: Steve Conklin <sconklin@canonical.com>
Signed-off-by: Steve Conklin <sconklin@canonical.com>