drm/debugfs: also take per device driver features into account

Use drm_core_check_all_features() to ensure both the driver features and
the per-device driver features are taken into account when registering
debugfs files.

v3:
- files[i].driver_features == 0 actually means "don't care"

v2:
- use drm_core_check_all_features()

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200123124801.14958-2-jani.nikula@intel.com