refactor: Move drivers into properly module.

* Align our driver module layout to properly match Zephyr conventions,
  allowing proper CMake setup to amend the library for each type of driver.

app/module/drivers/sensor/Kconfig

@@ -0,0 +1,9 @@
+# Copyright (c) 2020 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+if SENSOR
+
+rsource "battery/Kconfig"
+rsource "ec11/Kconfig"
+
+endif # SENSOR