ARM: OMAP: Fix relative includes for shared i2c.h file

As discussed on linux-arm-kernel, we want to avoid
relative includes for the arch/arm/*omap* shared code:

http://www.spinics.net/lists/linux-omap/msg80520.html

To fix this for the shared i2c.h, let's re-introduce
a minimal plat/i2c.h.

Note that drivers must not use this header as it will
break build for omap2+ CONFIG_MULTIPLATFORM builds.

Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/i2c.h

@@ -19,7 +19,7 @@
  *
  */
 
-#include "../plat-omap/i2c.h"
+#include <plat/i2c.h>
 
 #ifndef __MACH_OMAP2_I2C_H
 #define __MACH_OMAP2_I2C_H