AK3: unbreak anykernel scripts using flash_dtbo directly

tools/ak3-core.sh

@@ -457,6 +457,9 @@ flash_generic() {
   fi;
 }
 
+# flash_dtbo (backwards compatibility for flash_generic)
+flash_dtbo() { flash_generic dtbo; }
+
 ### write_boot (repack ramdisk then build, sign and write image, vendor_dlkm and dtbo)
 write_boot() {
   flash_generic vendor_dlkm; # TODO: move below boot once resizing is supported