Refactor global bindings, implement mod-tap.

* Use extra comptible = "zmk,behavior-global" to add
   behaviors to global bindings for event notification.
* Implement mod-tap, as a keymap binding and global one
  to skip tap if other keycode pressed while held.

app/dts/bindings/behaviors/zmk,behavior-mod-tap.yaml

@@ -0,0 +1,8 @@
+# Copyright (c) 2020, Pete Johanson
+# SPDX-License-Identifier: MIT
+
+description: Mod-Tap Beavhior
+
+compatible: "zmk,behavior-mod-tap"
+
+include: two_param.yaml

app/dts/bindings/zmk,global-bindings.yaml

@@ -1,9 +0,0 @@
-description: |
-  Specify the the global behaviors bound to state changes
-
-compatible: "zmk,global-bindings"
-
-properties:
-  bindings:
-    type: phandles
-    required: true