dm: move platform data headers to include/dm/platform_data

The platform_data definitions are generally referenced from both
drivers and board files.  That is why header files defining
platform_data sturectures are placed in "include" directory,
but our top level "include" directory is already too cluttered.

Let's collect platform_data definitions under the directory
"include/dm/platform_data" like Linux gathers ones around under
"include/linux/platform_data".

This commit moves two header files:

  include/serial_mxc.h -> include/dm/platform_data/serial_mxc.h
  include/serial_pl01x.h -> include/dm/platform_data/serial_pl01x.h

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/drivers/serial/serial_pl01x.c b/drivers/serial/serial_pl01x.c
index e6313ad..38dda91 100644
--- a/drivers/serial/serial_pl01x.c
+++ b/drivers/serial/serial_pl01x.c
@@ -17,7 +17,7 @@
 #include <watchdog.h>
 #include <asm/io.h>
 #include <serial.h>
-#include <serial_pl01x.h>
+#include <dm/platform_data/serial_pl01x.h>
 #include <linux/compiler.h>
 #include "serial_pl01x_internal.h"