test_firmware: test three firmware kernel configs using a proc knob

Since we now have knobs to twiddle what used to be set on kernel
configurations we can build one base kernel configuration and modify
behaviour to mimic such kernel configurations to test them.

Provided you build a kernel with:

CONFIG_TEST_FIRMWARE=y
CONFIG_FW_LOADER=y
CONFIG_FW_LOADER_USER_HELPER=y
CONFIG_IKCONFIG=y
CONFIG_IKCONFIG_PROC=y

We should now be able test all possible kernel configurations
when FW_LOADER=y. Note that when FW_LOADER=m we just don't provide
the built-in functionality of the built-in firmware.

If you're on an old kernel and either don't have /proc/config.gz
(CONFIG_IKCONFIG_PROC) or haven't enabled CONFIG_FW_LOADER_USER_HELPER
we cannot run these dynamic tests, so just run both scripts just
as we used to before making blunt assumptions about your setup
and requirements exactly as we did before.

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>