dm: gpio: Add of-platdata support

Add support for accessing GPIOs using of-plata. This uses the same
mechanism as for clocks, but allows use of the xlate() method so that
the driver can interpret the parameters.

Update the condition for GPIO_HOG so that it is not built into SPL,
since it needs SPL_OF_REAL which is not enabled in sandbox_spl.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/gpio/sandbox_test.c

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Sandbox driver for testing GPIOs with of-platdata
+ *
+ * Copyright 2021 Google LLC
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <asm-generic/gpio.h>
+
+static const struct udevice_id sandbox_gpio_test_ids[] = {
+	{ .compatible = "sandbox,gpio-test" },
+	{ }
+};
+
+U_BOOT_DRIVER(sandbox_gpio_test) = {
+	.name = "sandbox_gpio_test",
+	.id = UCLASS_MISC,
+	.of_match = sandbox_gpio_test_ids,
+};