x86: Add a clock driver for Intel devices

So far we have avoided adding a clock driver for Intel devices. But the
Designware I2C driver needs a different clock (133MHz) on Intel devices
than on others (166MHz). Add a simple driver that provides this
information.

This driver can be expanded later as needed.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

drivers/clk/intel/clk_intel.c

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2019 Google LLC
+ * Written by Simon Glass <sjg@chromium.org>
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <clk-uclass.h>
+#include <dt-bindings/clock/intel-clock.h>
+
+static ulong intel_clk_get_rate(struct clk *clk)
+{
+	ulong rate;
+
+	switch (clk->id) {
+	case CLK_I2C:
+		/* Hard-coded to 133MHz on current platforms */
+		return 133333333;
+	default:
+		return -ENODEV;
+	}
+
+	return rate;
+}
+
+static struct clk_ops intel_clk_ops = {
+	.get_rate	= intel_clk_get_rate,
+};
+
+static const struct udevice_id intel_clk_ids[] = {
+	{ .compatible = "intel,apl-clk" },
+	{ }
+};
+
+U_BOOT_DRIVER(clk_intel) = {
+	.name		= "clk_intel",
+	.id		= UCLASS_CLK,
+	.of_match	= intel_clk_ids,
+	.ops		= &intel_clk_ops,
+};