tests/functional: Add a functional test for the collie board

tests/functional: Add a functional test for the collie board

Add a functional test for the collie board that uses the kernel and
rootfs provided by Guenter Roeck in the linux-test-downloads repo:
 https://github.com/groeck/linux-test-downloads/

This just boots Linux with a userspace that immediately reboots
the board, so we wait for the reboot log line.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-id: 20241017163247.711244-2-peter.maydell@linaro.org