Add a mock kscan driver, working native_posix.

* Unified logging to one module.
* Mock kscan driver that simulates events.
* Working native_posix board target for testing.

boards/native_posix.conf

@@ -0,0 +1,8 @@
+CONFIG_ZMK_KSCAN_MOCK_DRIVER=y
+CONFIG_KSCAN=n
+CONFIG_KSCAN_GPIO=n
+CONFIG_GPIO=n
+CONFIG_ZMK_BLE=n
+CONFIG_LOG=y
+CONFIG_KSCAN_LOG_LEVEL_DBG=y
+CONFIG_ZMK_LOG_LEVEL_DBG=y

boards/native_posix.overlay

@@ -0,0 +1,47 @@
+#include <dt-bindings/zmk/keys.h>
+#include <zmk/kscan-mock.h>
+
+/ {
+	chosen {
+		zmk,kscan = &kscan0;
+		zmk,keymap = &keymap0;
+	};
+
+	kscan0: kscan {
+		compatible = "zmk,kscan-mock";
+		label = "KSCAN_MOCK0";
+
+		rows = <2>;
+		columns = <2>;
+		events = <ZMK_MOCK_PRESS(0,0,800) ZMK_MOCK_RELEASE(0,0,800)>;
+	};
+
+	keymap0: keymap {
+		compatible = "zmk,keymap";
+		label ="Default keymap";
+		layers = <&default &lower &raise>;
+	};
+
+	layers {
+		compatible = "zmk,layers";
+
+		default: layer_0 {
+			label = "DEFAULT";
+			keys =
+	<
+	KC_A KC_B
+	KC_C KC_D
+	>;
+		};
+
+		lower: layer_1 {
+			label = "LOWER";
+			keys = <KC_D KC_C ZC_TRNS ZC_TRNS>;
+		};
+
+		raise: layer_2 {
+			label = "RAISE";
+			keys = <KC_C KC_D ZC_TRNS ZC_TRNS>;
+		};
+	};
+};