selftests: media_tests: return Kselftest Skip code for skipped tests

When media_tests test is skipped because of unmet dependencies and/or
unsupported configuration, it exits with error which is treated as a
fail by the Kselftest framework. This leads to false negative result
even when the test could not be run.

Change it to return kselftest skip code when a test gets skipped to
clearly report that the test could not be run.

Change it to use ksft_exit_skip() when the test is skipped.

Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>

selftests: media_tests: Add SPDX license identifier

Replace GPL license statement with SPDX GPL-2.0 license identifier.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

selftests: add media_device_open test

Add a new media test to open, run ioctl, and close the media device file.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>