board: rockchip: Add minimal generic RK3528 board

Add a minimal generic RK3528 board that only have eMMC and SD-card
enabled. This defconfig can be used to boot from eMMC or SD-card on most
RK3528 boards that follow reference board design.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
5 files changed