plat/arm/fvp: Support performing SDEI platform setup in runtime ...

This patch introduces dynamic configuration for SDEI setup and is supported
when the new build flag SDEI_IN_FCONF is enabled. Instead of using C arrays
and processing the configuration at compile time, the config is moved to
dts files. It will be retrieved at runtime during SDEI init, using the fconf
layer.

Change-Id: If5c35a7517ba00a9f258d7f3e7c8c20cee169a31
Signed-off-by: Balint Dobszay <balint.dobszay@arm.com>
Co-authored-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>