oniro-openharmony-linux.conf: Add MUSL_LDSO_PATHS distro variable

This variable holds the system library folders used by OpenHarmony. It
will be used to generate the file /etc/ld-musl-${MUSL_LDSO_ARCH}.path.
It will also be used to do a sanity check and verify that all
/lib/module/* subfolders are parts of this musl ldso file.

Signed-off-by: Thierry Escande <thierry.escande@huawei.com>