drm: fix build errors with drm_print.h

drm_print.h requires <drm/drm.h> to fix build when macros are used.
Pull in the header file in drm_print.h so users do not have to do it.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190609220757.10862-2-sam@ravnborg.org

include/drm/drm_print.h

@@ -32,6 +32,8 @@
 #include <linux/device.h>
 #include <linux/debugfs.h>
 
+#include <drm/drm.h>
+
 /**
  * DOC: print
  *