move drivers/mfd/*.h to include/linux/mfd

So drivers like collie_battery driver can use
those files easier.
diff --git a/drivers/mfd/ucb1x00-assabet.c b/drivers/mfd/ucb1x00-assabet.c
index 86fed48..cea9da6 100644
--- a/drivers/mfd/ucb1x00-assabet.c
+++ b/drivers/mfd/ucb1x00-assabet.c
@@ -14,10 +14,10 @@
 #include <linux/fs.h>
 #include <linux/proc_fs.h>
 #include <linux/device.h>
+#include <linux/mfd/ucb1x00.h>
 
 #include <mach/dma.h>
 
-#include "ucb1x00.h"
 
 #define UCB1X00_ATTR(name,input)\
 static ssize_t name##_show(struct device *dev, struct device_attribute *attr, \