drm: Build drm_irq.o only if CONFIG_DRM_LEGACY has been set

All code in drm_irq.o is for legacy UMs drivers. Only build and link
the file if CONFIG_DRM_LEGACY has been enabled.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20211020131941.15367-2-tzimmermann@suse.de

drivers/gpu/drm/Makefile

@@ -4,7 +4,7 @@
 # Direct Rendering Infrastructure (DRI) in XFree86 4.1.0 and higher.
 
 drm-y       :=	drm_aperture.o drm_auth.o drm_cache.o \
-		drm_file.o drm_gem.o drm_ioctl.o drm_irq.o \
+		drm_file.o drm_gem.o drm_ioctl.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_displayid.o \
@@ -21,8 +21,8 @@ drm-y       :=	drm_aperture.o drm_auth.o drm_cache.o \
 		drm_managed.o drm_vblank_work.o
 
 drm-$(CONFIG_DRM_LEGACY) += drm_agpsupport.o drm_bufs.o drm_context.o drm_dma.o \
-			    drm_legacy_misc.o drm_lock.o drm_memory.o drm_scatter.o \
-			    drm_vm.o
+			    drm_irq.o drm_legacy_misc.o drm_lock.o drm_memory.o \
+			    drm_scatter.o drm_vm.o
 drm-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o
 drm-$(CONFIG_COMPAT) += drm_ioc32.o
 drm-$(CONFIG_DRM_GEM_CMA_HELPER) += drm_gem_cma_helper.o

drivers/gpu/drm/drm_irq.c

@@ -66,7 +66,6 @@
 
 #include "drm_internal.h"
 
-#if IS_ENABLED(CONFIG_DRM_LEGACY)
 static int drm_legacy_irq_install(struct drm_device *dev, int irq)
 {
 	int ret;
@@ -203,4 +202,3 @@ int drm_legacy_irq_control(struct drm_device *dev, void *data,
 		return -EINVAL;
 	}
 }
-#endif