drm/i915: Replace the VLV/CHV eDP reboot notifier with the .shutdown() hook

drm/i915: Replace the VLV/CHV eDP reboot notifier with the .shutdown() hook

Currently VLV/CHV use a reboot notifier to make sure the panel
power cycle delay isn't violated across a system reboot. Replace
that with the new encoder .shutdown() hook.

And let's also stop overriding the power cycle delay with the
max value. No idea why the current code does that. The already
programmed delay should be correct.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201001151640.14590-3-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>