drm/i915: Disable runtime power management during shutdown

drm/i915: Disable runtime power management during shutdown

commit 7962893ecb853aa7c8925ce237ab6c4274cfc1c7 upstream.

At least on some TGL platforms PUNIT wants to access some display HW
registers, but it doesn't handle display power management (disabling DC
states as required) and so this register access will lead to a hang. To
prevent this disable runtime power management for poweroff and reboot.

v2:
- Add code comment clarifying the requirement of display power states.
  (Ville)

Reported-and-tested-by: Khaled Almahallawy <khaled.almahallawy@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Khaled Almahallawy <khaled.almahallawy@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210127181909.128094-1-imre.deak@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>