gdsys: mpc8308: Don't use manual RAM config if RAM driver is active

The "manual" RAM configuration should not be used if the DM RAM driver
is active, hence, disable the code if the CONFIG_MPC83XX_SDRAM config
variable is defined.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/board/gdsys/mpc8308/sdram.c b/board/gdsys/mpc8308/sdram.c
index 3eb0e37..2a77fed 100644
--- a/board/gdsys/mpc8308/sdram.c
+++ b/board/gdsys/mpc8308/sdram.c
@@ -11,6 +11,8 @@
  * board\freescale\mpc8315erdb\sdram.c
  */
 
+#ifndef CONFIG_MPC83XX_SDRAM
+
 #include <common.h>
 #include <mpc83xx.h>
 #include <spd_sdram.h>
@@ -81,3 +83,5 @@
 
 	return 0;
 }
+
+#endif /* !CONFIG_MPC83XX_SDRAM */