board: rockchip: Add minimal generic RK3328 board

Add a minimal generic RK3328 board that only have eMMC, SDMMC, SPI flash
and USB OTG enabled. This defconfig can be used to boot from eMMC,
SD-card or SPI flash on most RK3328 boards that follow reference board
design.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Christopher Obbard <christopher.obbard@linaro.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
6 files changed