board: rockchip: Add Radxa Compute Module 3 IO Board

Radxa Compute Module 3(CM3) IO board an application board from Radxa
and is compatible with Raspberry Pi CM4 IO form factor.

Radxa CM3 needs to mount on top of this IO board in order to create
complete Radxa CM3 IO board platform.

Add support for Radxa CM3 IO Board defconfig and -u-boot.dtsi

Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>