AMD Southstation: Fix final warning

Changes:
 - Add #include of delay.h in mainboard.c to pick up declaration of
   mdelay function.

Notes:
 - This fixes this warning:
   mainboard.c:69, GNU Compiler 4 (gcc), Priority: Normal
   implicit declaration of function 'mdelay' [-Wimplicit-function-declaration]

Change-Id: I72f333cd87215a7fc1e62d1d7ee4b2395444b03e
Signed-off-by: Martin Roth <martin.roth@se-eng.com>
Reviewed-on: http://review.coreboot.org/2501
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/amd/south_station/mainboard.c

@@ -24,6 +24,7 @@
 #include <cpu/x86/msr.h>
 #include <cpu/amd/mtrr.h>
 #include <device/pci_def.h>
+#include <delay.h>
 #include "SBPLATFORM.h" 	/* Platfrom Specific Definitions */