Kirkwood: bugfix: broken early console messages

It has been observed that, the complete u-boot banner
does not appear on the console when the system is booted
from NAND/NOR/SPI flash.

This patch fixes this issue on all Marvell boards by adding
board_early_init_f() support

Signed-off-by: Prafulla Wadaskar <prafulla@marvell.com>