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/behaviors/hid.dtsi

@@ -1,7 +1,7 @@
 / {
 	behaviors {
 		hid_behavior: behavior_hid {
-			compatible = "zmk,behavior-hid";
+			compatible = "zmk,behavior-hid", "zmk,behavior-global";
 			label = "HID";
 			#binding-cells = <0>;
 		};

app/dts/behaviors/keymap.dtsi

@@ -1,7 +1,7 @@
 / {
 	behaviors {
 		keymap_behavior: behavior_keymap {
-			compatible = "zmk,behavior-keymap";
+			compatible = "zmk,behavior-keymap", "zmk,behavior-global";
 			label = "KEYMAP";
 			#binding-cells = <0>;
 		};

app/dts/behaviors/mod_tap.dtsi

@@ -0,0 +1,9 @@
+/ {
+	behaviors {
+		mt: behavior_mod_tap {
+			compatible = "zmk,behavior-mod-tap", "zmk,behavior-global";
+			label = "MOD_TAP";
+			#binding-cells = <2>;
+		};
+	};
+};

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