Ignore custom firmware loading and cancellation tests on older
kernel releases, which do not support this feature.

Fixes: 061132d2 ("test_firmware: add test custom fallback trigger")
Reviewed-by: NSumit Semwal <sumit.semwal@linaro.org>
Acked-by: NLuis R. Rodriguez <mcgrof@kernel.org>
Acked-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NAmit Pundir <amit.pundir@linaro.org>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>