test:dfu: Add test scripts for testing DFU regression

This commit adds test scripts for testing if any commit has introduced
regression to the DFU subsystem.

It uses md5 to test if sent and received file is correct.
The test detailed description is available at README file.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
diff --git a/test/dfu/README b/test/dfu/README
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+DFU TEST CASE DESCRIPTION:
+
+The prerequisites for running this script are assured by dfu_gadget_test_init.sh.
+In this file user is able to generate their own set of test files by altering
+the default set of TEST_FILES_SIZES variable.
+The dfu_gadget_test_init.sh would generate test images only if they are not
+already generated.
+
+Moreover, on a target device the "dfu_alt_info" env variable should be extended
+to have "dfu_test.bin fat 0 6;" \ entry ([1]). For reference please consult the
+config file for TRATS/TRATS2 devices (./include/configs/trats{2}.h)
+
+One can use fat, ext4 or any other supported file system, which can be
+created in a convenient way with exporting partitions via UMS (ums 0 mmc 0)
+and using standard tools on host (like mkfs.ext4).
+
+Example usage:
+1. On the target:
+   env default -a
+   dfu 0 mmc 0
+2. On the host:
+   ./dfu_gadget_test.sh 11 [test_file]
+
+where 11 is the mumber of alt setting corresponding to entry [1] and [test_file]
+is an optional parameter, with which one can explicitly indicate the test file
+to be used.
+
+The number of the alt setting entry can be obtained with dfu-util -l command.
+In its output one should look for the 'name="dfu_test1.bin"' and corresponding
+alt=11.