Initial working Clueboard California Macropad w/ proton-c fixes

* Basic Clueboard Californai Macropad shield definition.
* New "direct" KSCAN driver that supports non-matrix direct
  wiring for switches, needed for macropad that doesn't have
  a matrix at all.
* Some renames for existing KSCAN GPIO driver to make the implied
  "matrix" part explicit.

app/drivers/zephyr/dts/bindings/zmk,kscan-gpio-matrix.yaml

@@ -0,0 +1,25 @@
+# Copyright (c) 2020, Pete Johanson
+# SPDX-License-Identifier: MIT
+
+description: GPIO keyboard matrix controller
+
+compatible: "zmk,kscan-gpio-matrix"
+
+include: kscan.yaml
+
+properties:
+  row-gpios:
+    type: phandle-array
+    required: true
+  col-gpios:
+    type: phandle-array
+    required: true
+  debounce-period:
+    type: int
+    default: 5
+  diode-direction:
+    type: string
+    default: row2col
+    enum:
+      - row2col
+      - col2row