fortunately you don't have to compile the kernel completely, just generate a single
dtb in the sources
and that diff --git is just part of the output of a git diff, you need to: dnf install
patch dtc gcc
cd /usr/src/kernel/4.16.3-300.fc28.aarch64/
patch -p1 < /tmp/bcm283x.dtsi.patch
cd arch/arm/boot/dts/
gcc -E -I../../../../include -P -x assembler-with-cpp bcm2837-rpi-3-b.dts | dtc -I dts -O
dtb -o bcm2837-rpi-3-b.dtb -
cp bcm2837-rpi-3-b.dtb /boot/dtb-4.16.3-300.fc28.aarch64/broadcom/bcm2837-rpi-3-b.dtb
reboot, and then you should have two /dev/spi*