ARM: S5P64X0: Explicitly include linux/serial_s3c.h in mach/pm-core.h

This patch fixes compilation failure due to missing explicit inclusion
of linux/serial_s3c.h in mach/pm-core.h, which contains definitions
required for further code in this header.
Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/mach-s5p64x0/include/mach/pm-core.h

@@ -12,6 +12,8 @@
  * published by the Free Software Foundation.
  */
 
+#include <linux/serial_s3c.h>
+
 #include <mach/regs-gpio.h>
 
 static inline void s3c_pm_debug_init_uart(void)