nitro_enclaves: Add KUnit tests setup for the misc device functionality

Add the initial setup for the KUnit tests that will target the Nitro
Enclaves misc device functionality.

Reviewed-by: Andra Paraschiv <andraprs@amazon.com>
Signed-off-by: Longpeng <longpeng2@huawei.com>
Link: https://lore.kernel.org/r/20211107140918.2106-4-longpeng2@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>