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>
