BuildSystem: Add support for building initrd image

This is nice for testing when there isn't xhci controller available or
my usb stack fails :)

script/config.sh

@@ -28,6 +28,10 @@ if [[ -z $BANAN_UEFI_BOOT ]]; then
 	export BANAN_UEFI_BOOT=0
 fi
 
+if [[ -z $BANAN_INITRD ]]; then
+	export BANAN_INITRD=0
+fi
+
 if [[ -z $BANAN_BOOTLOADER ]]; then
 	export BANAN_BOOTLOADER='BANAN'
 fi