igt/pm_backlight: Skip if pm is not supported

If we cannot do runtime suspend, testing it's impact on the backlight is
moot. Simply skip on systems that cannot runtime suspend.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107789
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107790
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107794
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
1 file changed