powerpc/ddr: fix fsl_ddr_get_dimm_params compile error

fsl_ddr_get_dimm_params() should be wrapped by
CONFIG_SYS_DDR_RAW_TIMING, otherwise, when using fixed_sdram() instead of
using SPD, it will cause compile error.
Signed-off-by: NShaohui Xie <Shaohui.Xie@freescale.com>
Acked-by: NYork Sun <yorksun@freescale.com>
Signed-off-by: NAndy Fleming <afleming@freescale.com>

arch/powerpc/cpu/mpc8xxx/ddr/main.c

@@ -366,7 +366,7 @@ fsl_ddr_compute(fsl_ddr_info_t *pinfo, unsigned int start_step,
 			}
 		}
 
-#else
+#elif defined(CONFIG_SYS_DDR_RAW_TIMING)
 	case STEP_COMPUTE_DIMM_PARMS:
 		for (i = 0; i < CONFIG_NUM_DDR_CONTROLLERS; i++) {
 			for (j = 0; j < CONFIG_DIMM_SLOTS_PER_CTLR; j++) {