lib: Add asf4 as a submodule.

dpgeorge · dpgeorge · commit 875af757bd24 · 2019-07-01T17:18:44.000+10:00
diff --git a/.gitmodules b/.gitmodules
@@ -21,3 +21,6 @@
 [submodule "lib/mbedtls"]
 	path = lib/mbedtls
 	url = https://github.com/ARMmbed/mbedtls.git
+[submodule "lib/asf4"]
+	path = lib/asf4
+	url = https://github.com/adafruit/asf4
diff --git a/lib/asf4 b/lib/asf4
@@ -0,0 +1 @@
+Subproject commit d270f79aa16dd8fd4ae3b6c14544283dcb992e9c
