ARM: OMAP2+: Include soc.h to drm.c to fix compiling

I needed this when compiling for pandaboard.

The reason this is needed is that we are now using
omap_initcalls to keep them multiplatform safe.
Signed-off-by: NAndré Hentschel <nerv@dawncrow.de>
[tony@atomide.com: updated comments]
Signed-off-by: NTony Lindgren <tony@atomide.com>
Signed-off-by: NOlof Johansson <olof@lixom.net>

arch/arm/mach-omap2/drm.c

@@ -27,6 +27,7 @@
 
 #include "omap_device.h"
 #include "omap_hwmod.h"
+#include "soc.h"
 
 #if defined(CONFIG_DRM_OMAP) || (CONFIG_DRM_OMAP_MODULE)