Travis-CI: Add job for running test.py on qemu_arm64

The corresponding changes in the uboot-test-hooks repo are:

https://github.com/swarren/uboot-test-hooks/pull/15



Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Reviewed-by: Tom Rini <trini@konsulko.com>