arm: kirkwood: Pogoplug-V4 : Add board implementation files

Add board header, defconfig, and implementation files for Pogoplug V4.

Signed-off-by: Tony Dinh <mibodhi@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Pali Rohár <pali@kernel.org>
6 files changed