sysota: cleandirs make-based build tree

This fixes build failure with an existing build tree:

    ln: failed to create symbolic link 'Makefile': File exists

The CI process never caught this and the developer who introduced the
recipe uses rm_work locally, so this was not seen during daily
development.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>