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/kscan/kscan_gpio.c

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "kscan_gpio.h"
+
+#include <stdlib.h>
+
+static int compare_ports(const void *a, const void *b) {
+    const struct kscan_gpio *gpio_a = a;
+    const struct kscan_gpio *gpio_b = b;
+
+    return gpio_a->spec.port - gpio_b->spec.port;
+}
+
+void kscan_gpio_list_sort_by_port(struct kscan_gpio_list *list) {
+    qsort(list->gpios, list->len, sizeof(list->gpios[0]), compare_ports);
+}
+
+int kscan_gpio_pin_get(const struct kscan_gpio *gpio, struct kscan_gpio_port_state *state) {
+    if (gpio->spec.port != state->port) {
+        state->port = gpio->spec.port;
+
+        const int err = gpio_port_get(state->port, &state->value);
+        if (err) {
+            return err;
+        }
+    }
+
+    return (state->value & BIT(gpio->spec.pin)) != 0;
+}