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-omap1/i2c.c

@@ -23,7 +23,7 @@
 #include <mach/mux.h>
 #include "soc.h"
 
-#include "../plat-omap/i2c.h"
+#include <plat/i2c.h>
 
 #define OMAP_I2C_SIZE		0x3f
 #define OMAP1_I2C_BASE		0xfffb3800