drm/i915/dsi: Move MIPI_SEQ_POWER_ON/OFF calls together with pmic gpio calls

Now that we are no longer bound to the drm_panel_ callbacks, call
MIPI_SEQ_POWER_ON/OFF at the proper place.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Bob Paauwe <bob.j.paauwe@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1488374106-4949-4-git-send-email-jani.nikula@intel.com