In preparation for FAP-220-B support, rename ar934x_fortinet_loader.dtsi to arxxxx_fortinet_loader.dtsi, to avoid confusion, as FAP-220-B shares flash layout with FAP-221-B exactly despite different SoC. While at that, add a label to U-boot partition to allow for nvmem MAC binding in future. Signed-off-by: Lech Perczak <lech.perczak@gmail.com>