Add rpmsg-echo-test example

rpmsg-echo-test example demonstrates how to write linux userspace
application that uses rpmsg devices in kernel space.
This application sends pre-defined payload to remote processor
firmware and waits for remote processor to send same payload back.
It then verifies received payload integrity. Number of packets to
send to remote processor can be configured from command line

Signed-off-by: Tanmay Shah <tanmay.shah@amd.com>

examples/linux/rpmsg-echo-test/LICENSE

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+Software License Agreement (BSD License)
+========================================
+
+Copyright (c) 2014, Mentor Graphics Corporation. All rights reserved.
+Copyright (c) 2015 - 2016 Xilinx, Inc. All rights reserved.
+Copyright (c) 2016 Freescale Semiconductor, Inc. All rights reserved
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice,
+   this list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+3. The names of its contributors may not be used to endorse or promote
+   products derived from this software without specific prior written
+   permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+

examples/linux/rpmsg-echo-test/Makefile

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+
+APP = echo_test
+APP_OBJS = echo_test.o
+
+# Add any other object files to this list below
+
+
+all: $(APP)
+
+$(APP): $(APP_OBJS)
+	$(CC) $(LDFLAGS) -o $@ $(APP_OBJS) $(LDLIBS)
+
+clean:
+	rm -rf $(APP) *.o
+
+%.o: %.c
+	$(CC) -c $(CFLAGS) -o $@ $<
+

examples/linux/rpmsg-echo-test/README

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+echo_test
+
+Description:
+  This demo uses linux kernel rpmsg framework to send large data buffer to remote
+  processor and validates integrity of received buffer from remote processor.
+  If buffer data does not match, then number of different bytes are reported on
+  console
+
+Remoteproc firmware for Xilinx ZynqMP platform:
+  https://github.com/Xilinx/embeddedsw/tree/xlnx_rel_v2022.1/lib/sw_apps/openamp_echo_test