ARM: davinci: fix build breakage with DEBUG_LL

commit fcf7157b ("ARM: davinci: serial: get rid of davinci_uart_config")
introduced build breakage because of a misplaced
header file include which cause a bunch of errors when
the file is included in assembly code (like debug-macro.S)

Fix the build breakage.
Reported-by: Alexander Holler <holler@ahsoftware.de>
Tested-by: Alexander Holler <holler@ahsoftware.de>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>

arch/arm/mach-davinci/include/mach/serial.h

@@ -15,8 +15,6 @@
 
 #include <mach/hardware.h>
 
-#include <linux/platform_device.h>
-
 #define DAVINCI_UART0_BASE	(IO_PHYS + 0x20000)
 #define DAVINCI_UART1_BASE	(IO_PHYS + 0x20400)
 #define DAVINCI_UART2_BASE	(IO_PHYS + 0x20800)
@@ -39,6 +37,8 @@
 #define UART_DM646X_SCR_TX_WATERMARK	0x08
 
 #ifndef __ASSEMBLY__
+#include <linux/platform_device.h>
+
 extern int davinci_serial_init(struct platform_device *);
 #endif