arm: add support of Kirkwood based board SUEN8

The Kirwood based SUEN8 board from Keymile is at this stage
the same than the suen3 board. This patch adds the board
support for the suen8.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Signed-off-by: Heiko Schocher <hs@denx.de>
cc: Prafulla Wadaskar <prafulla@marvell.com>