tools: kwboot: Update references with public links

Public documents about BootROM of some Marvell SoCs are available in the
public Web Archive. Put this information into source code.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>
Tested-by: Stefan Roese <sr@denx.de>