configs: fwu: re-enable FWU configs

Now that support for FWU metadata version 2 has been added, the
feature can be enabled on platforms which had enabled it. A new config
symbol for selecting the metadata version for the platform is also
being added.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Tested-by: Michal Simek <michal.simek@amd.com>