rockchip: rk3328: add SPL board file support

rockchip: rk3328: add SPL board file support

rk3328 SPL is locate at dram, so do not have strict size limit,
suppose to enable storage media controller driver, load ATF and
U-Boot, then boot into ATF.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
[cherry picked from https://github.com/rockchip-linux/u-boot/commit/4ebe3968b683190cb8e5741aa7227b4fa7497874 with minor modifications]
Signed-off-by: Matwey V. Kornilov <matwey.kornilov@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>