mfd: Fix twl4030-core build

Fixes:
drivers/mfd/twl4030-core.c:657: error: implicit declaration of function
'cpu_is_omap2430'

Not the nicest fix, but this should be improved by a better OMAP clock API
implementation.
Signed-off-by: NSamuel Ortiz <sameo@openedhand.com>

drivers/mfd/twl4030-core.c

@@ -38,6 +38,9 @@
 #include <linux/i2c.h>
 #include <linux/i2c/twl4030.h>
 
+#ifdef CONFIG_ARM
+#include <mach/cpu.h>
+#endif
 
 /*
  * The TWL4030 "Triton 2" is one of a family of a multi-function "Power