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>
