generate_config: Use eyaml to decrypt secret values

generate_config: Use eyaml to decrypt secret values

Note: IDF data encryption is not supported. Supporting that is
trivial, but it leads to slightly more complicated code, plus it
breaks support for multiline scalar encrypted data in the PDF ('>'),
forcing us to define each encrypted value as inline string.

While at it, fix silly limitation of jinja2 path residing in a subdir
of CWD.

Change-Id: I441ec754d8b6e4aad2ed73aba0b9b18ed65f05f4
Signed-off-by: agardner <agardner@linuxfoundation.org>
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
(cherry picked from commit d2307b5afbf13644bfe6722018ef1975e92680d1)