drivers: introduce Secure Monitor uclass

At the moment, we don't have a common API for working with
SM, only the smc_call() function. This approach is not generic
and difficult to configure and maintain.

This patch adds UCLASS_SM with the generic API:

- sm_call()
- sm_call_write()
- sm_call_read()

These functions operate with struct pt_regs, which describes
Secure Monitor arguments.

Signed-off-by: Alexey Romanov <avromanov@salutedevices.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Link: https://lore.kernel.org/r/20230921081346.22157-2-avromanov@salutedevices.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>

drivers/sm/Kconfig

@@ -0,0 +1,2 @@
+config SM
+	bool "Enable Secure Monitor driver support"

drivers/sm/Makefile

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-y += sm-uclass.o

drivers/sm/sm-uclass.c

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2023 SberDevices, Inc.
+ *
+ * Author: Alexey Romanov <avromanov@salutedevices.com>
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <errno.h>
+#include <sm-uclass.h>
+
+static const struct sm_ops *get_sm_ops(struct udevice *dev)
+{
+	return (const struct sm_ops *)dev->driver->ops;
+}
+
+int sm_call(struct udevice *dev, u32 cmd, s32 *ret, struct pt_regs *args)
+{
+	const struct sm_ops *ops = get_sm_ops(dev);
+
+	if (ops->sm_call)
+		return ops->sm_call(dev, cmd, ret, args);
+
+	return -ENOSYS;
+}
+
+int sm_call_read(struct udevice *dev, void *buffer, size_t size,
+		 u32 cmd, struct pt_regs *args)
+{
+	const struct sm_ops *ops = get_sm_ops(dev);
+
+	if (ops->sm_call_read)
+		return ops->sm_call_read(dev, buffer, size, cmd,
+					 args);
+
+	return -ENOSYS;
+}
+
+int sm_call_write(struct udevice *dev, void *buffer, size_t size,
+		   u32 cmd, struct pt_regs *args)
+{
+	const struct sm_ops *ops = get_sm_ops(dev);
+
+	if (ops->sm_call_write)
+		return ops->sm_call_write(dev, buffer, size, cmd,
+					  args);
+
+	return -ENOSYS;
+}
+
+UCLASS_DRIVER(sm) = {
+	.name           = "sm",
+	.id             = UCLASS_SM,
+};