Passed the address of fw_config instead of soc_fw_config
as arg1 to BL31 from BL2 for ARM fvp platform.

BL31 then retrieve load-address of other device trees
from fw_config device tree.

Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: Ib7e9581cd765d76111dcc3b7e0dafc12503c83c1