fconf: Clean Arm IO

Merge the previously introduced arm_fconf_io_storage into arm_io_storage. This
removes the duplicate io_policies and functions definition.

This patch:
- replace arm_io_storage.c with the content of arm_fconf_io_storage.c
- rename the USE_FCONF_BASED_IO option into ARM_IO_IN_DTB.
- use the ARM_IO_IN_DTB option to compile out io_policies moved in dtb.
- propagate DEFINES when parsing dts.
- use ARM_IO_IN_DTB to include or not uuid nodes in fw_config dtb.
- set the ARM_IO_IN_DTB to 0 by default for fvp. This ensure that the behavior
  of fvp stays the same as it was before the introduction of fconf.

Change-Id: Ia774a96d1d3a2bccad29f7ce2e2b4c21b26c080e
Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index f138feb..e53f714 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -622,8 +622,8 @@
    exposing a virtual filesystem interface through BL31 as a SiP SMC function.
    Default is 0.
 
--  ``USE_FCONF_BASED_IO``: This flag determines whether to use IO based on the
-   firmware configuration framework. This allows moving the io_policies into a
+-  ``ARM_IO_IN_DTB``: This flag determines whether to use IO based on the
+   firmware configuration framework. This will move the io_policies into a
    configuration device tree, instead of static structure in the code base.