drm: fix Kconfig dependency

fixup DRM/AGP Kconfig inter-dependency...

From: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/drm/Kconfig

@@ -6,6 +6,7 @@
 #
 config DRM
 	tristate "Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)"
+	depends on AGP || AGP=n
 	help
 	  Kernel-level support for the Direct Rendering Infrastructure (DRI)
 	  introduced in XFree86 4.0. If you say Y here, you need to select