configs: enable UNIT_TEST on qemu_arm_defconfig

configs: enable UNIT_TEST on qemu_arm_defconfig

The lib_test_uuid_to_le test fails on 32-bit systems. But we never caught
this in our CI because we never ran any of our C unit tests on 32-bit.

Enable CONFIG_UNIT_TEST on qemu_arm_defconfig.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>