arm64: dts: socfpga: agilex: move firmware out of soc node

The "soc" node is supposed to have only MMIO children, so move the
firmware/svc node to top level to fix dtc W=1 warnings like:

  socfpga_agilex.dtsi:663.12-673.5: Warning (simple_bus_reg): /soc@0/firmware: missing or empty reg/ranges property

The node should still be instantiated by drivers/of/platform.c, just
like in all other platforms.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>