drm/amdgpu: Drop DRIVER_USE_AGP

This doesn't do anything except auto-init drm_agp support when you
call drm_get_pci_dev(). Which amdgpu stopped doing with

commit b58c1131
Author: Alex Deucher <alexander.deucher@amd.com>
Date:   Fri Jun 2 17:16:31 2017 -0400

    drm/amdgpu: drop deprecated drm_get_pci_dev and drm_put_dev

No idea whether this was intentional or accidental breakage, but I
guess anyone who manages to boot a this modern gpu behind an agp
bridge deserves a price. A price I never expect anyone to ever collect
:-)

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Hawking Zhang <Hawking.Zhang@amd.com>
Cc: Xiaojie Yuan <xiaojie.yuan@amd.com>
Cc: Evan Quan <evan.quan@amd.com>
Cc: "Tianci.Yin" <tianci.yin@amd.com>
Cc: "Marek Olšák" <marek.olsak@amd.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: NEmil Velikov <emil.velikov@collabora.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c

@@ -1394,7 +1394,7 @@ amdgpu_get_crtc_scanout_position(struct drm_device *dev, unsigned int pipe,
 
 static struct drm_driver kms_driver = {
 	.driver_features =
-	    DRIVER_USE_AGP | DRIVER_ATOMIC |
+	    DRIVER_ATOMIC |
 	    DRIVER_GEM |
 	    DRIVER_RENDER | DRIVER_MODESET | DRIVER_SYNCOBJ |
 	    DRIVER_SYNCOBJ_TIMELINE,