rockchip: use dummy byte only enable OF_PLATDATA

Add a condition to determine the rk3288_sdram_channel size.

This patch fixes read sdram_channel property failed from DT on rk3288
boards, which not enable OF_PLATDATA.
Signed-off-by: NZiyuan Xu <xzy.xu@rock-chips.com>

arch/arm/include/asm/arch-rockchip/sdram.h

@@ -24,12 +24,16 @@ struct rk3288_sdram_channel {
 	u8 row_3_4;
 	u8 cs0_row;
 	u8 cs1_row;
+#if CONFIG_IS_ENABLED(OF_PLATDATA)
 	/*
 	 * For of-platdata, which would otherwise convert this into two
 	 * byte-swapped integers. With a size of 9 bytes, this struct will
 	 * appear in of-platdata as a byte array.
+	 *
+	 * If OF_PLATDATA enabled, need to add a dummy byte in dts.(i.e 0xff)
 	 */
 	u8 dummy;
+#endif
 };
 
 struct rk3288_sdram_pctl_timing {