fconf: Move platform io policies into fconf

Use the firmware configuration framework to store the io_policies
information inside the configuration device tree instead of the static
structure in the code base.

The io_policies required by BL1 can't be inside the dtb, as this one is
loaded by BL1, and only available at BL2.

This change currently only applies to FVP platform.

Change-Id: Ic9c1ac3931a4a136aa36f7f58f66d3764c1bfca1
Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>