config: create config/bootloaders directory

to help users know that this is where they can put custom bootloader
configs, just as other directories are created for them.

Gbp-Dch: Short

scripts/build/config

@@ -1178,6 +1178,7 @@ mkdir -p config/includes.installer
 mkdir -p config/packages.binary
 mkdir -p config/package-lists
 mkdir -p config/rootfs
+mkdir -p config/bootloaders
 
 cat > config/binary << EOF
 # config/binary - options for live-build(7), binary stage