fault-inject: export fault injection functions

Export symbols should_fail() and fault_create_debugfs_attr() in order
to let modules utilize the fault injection framework.

Signed-off-by: Per Forlin <per.forlin@linaro.org>
Acked-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Chris Ball <cjb@laptop.org>