drm: Build drm_memory.o only for legacy drivers

The file contains I/O-memory functions that are only used by legacy
drivers.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210112081035.6882-4-tzimmermann@suse.de

drivers/gpu/drm/Makefile

@@ -5,7 +5,7 @@
 
 drm-y       :=	drm_auth.o drm_cache.o \
 		drm_file.o drm_gem.o drm_ioctl.o drm_irq.o \
-		drm_memory.o drm_drv.o \
+		drm_drv.o \
 		drm_sysfs.o drm_hashtab.o drm_mm.o \
 		drm_crtc.o drm_fourcc.o drm_modes.o drm_edid.o \
 		drm_encoder_slave.o \
@@ -20,7 +20,8 @@ drm-y       :=	drm_auth.o drm_cache.o \
 		drm_client_modeset.o drm_atomic_uapi.o drm_hdcp.o \
 		drm_managed.o drm_vblank_work.o
 
-drm-$(CONFIG_DRM_LEGACY) += drm_legacy_misc.o drm_bufs.o drm_context.o drm_dma.o drm_scatter.o drm_lock.o
+drm-$(CONFIG_DRM_LEGACY) += drm_bufs.o drm_context.o drm_dma.o drm_legacy_misc.o drm_lock.o \
+		drm_memory.o drm_scatter.o
 drm-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o
 drm-$(CONFIG_DRM_VM) += drm_vm.o
 drm-$(CONFIG_COMPAT) += drm_ioc32.o