drm/i915: Wait for power cycle delay after turning off DSI panel power

drm/i915: Wait for power cycle delay after turning off DSI panel power

The power cycle delay starts _after_ turning off the panel power. Do the
msleep after frobbing the pmic panel power gpio.

Also toss in a FIXME about optimizing away needless waits.

Cc: Shobhit Kumar <shobhit.kumar@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Fixes: fc45e8219907 ("drm/i915: Use the CRC gpio for panel enable/disable")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1460996271-29795-1-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Shobhit Kumar <shobhit.kumar@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>