Revert "drm: Hack around CONFIG_AGP=m build failures"

Kbuild now supports <modname>-m variables.

This reverts commit 8fa884dc.
Signed-off-by: Michal Marek <mmarek@suse.cz>

drivers/gpu/drm/Makefile

@@ -21,8 +21,6 @@ drm-$(CONFIG_DRM_PANEL) += drm_panel.o
 drm-$(CONFIG_OF) += drm_of.o
 drm-$(CONFIG_AGP) += drm_agpsupport.o
 
-drm-y += $(drm-m)
-
 drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
 		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o
 drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o