ram: rockchip: Add basic support for RK3528

Add support for reading DRAM size information from PMUGRF os_reg18 reg.

Compared to most Rockchip SoCs the RK3528 use os_reg18 for DRAM info,
instead of os_reg2.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/mach-rockchip/sdram.c b/arch/arm/mach-rockchip/sdram.c
index f7d3282..aa3f47c 100644
--- a/arch/arm/mach-rockchip/sdram.c
+++ b/arch/arm/mach-rockchip/sdram.c
@@ -110,7 +110,8 @@
 	u8 i, j;
 
 	if (!IS_ENABLED(CONFIG_ROCKCHIP_RK3588) &&
-	    !IS_ENABLED(CONFIG_ROCKCHIP_RK3568))
+	    !IS_ENABLED(CONFIG_ROCKCHIP_RK3568) &&
+	    !IS_ENABLED(CONFIG_ROCKCHIP_RK3528))
 		return -ENOTSUPP;
 
 	if (!IS_ENABLED(CONFIG_ROCKCHIP_EXTERNAL_TPL))