misc: fastrpc: Add support for context Invoke method

This patch adds support to compute context invoke method on the
remote processor (DSP).
This involves setting up the functions input and output arguments,
input and output handles and mapping the dmabuf fd for the
argument/handle buffers.

The below diagram depicts invocation of a single method where the
client and objects reside on different processors. An object could
expose multiple methods which can be grouped together and referred
to as an interface.

,--------,        ,------,  ,-----------,  ,------,        ,--------,
|        | method |      |  |           |  |      | method |        |
| Client |------->| Stub |->| Transport |->| Skel |------->| Object |
|        |        |      |  |           |  |      |        |        |
`--------`        `------`  `-----------`  `------`        `--------`

Client:    Linux user mode process that initiates the remote invocation
Stub:      Auto generated code linked in with the user mode process that
           takes care of marshaling parameters
Transport: Involved in carrying an invocation from a client to an
           object. This involves two portions: 1) FastRPC Linux
           kernel driver that receives the remote invocation, queues
           them up and then waits for the response after signaling the
           remote side. 2) Service running on the remote side that
           dequeues the messages from the queue and dispatches them for
           processing.
Skel:      Auto generated code that takes care of un-marshaling
           parameters
Object:    Method implementation

Most of the work is derived from various downstream Qualcomm kernels.
Credits to various Qualcomm authors who have contributed to this code.
Specially Tharun Kumar Merugu <mtharu@codeaurora.org>
Co-developed-by: Thierry Escande <thierry.escande@linaro.org>
Signed-off-by: Thierry Escande <thierry.escande@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/uapi/misc/fastrpc.h

+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __QCOM_FASTRPC_H__
+#define __QCOM_FASTRPC_H__
+
+#include <linux/types.h>
+
+#define FASTRPC_IOCTL_INVOKE		_IOWR('R', 3, struct fastrpc_invoke)
+
+struct fastrpc_invoke_args {
+	__u64 ptr;
+	__u64 length;
+	__s32 fd;
+	__u32 reserved;
+};
+
+struct fastrpc_invoke {
+	__u32 handle;
+	__u32 sc;
+	__u64 args;
+};
+
+#endif /* __QCOM_FASTRPC_H__ */