soc: qom: add support to export socinfo id string

Some kernel modules may explicitly want to use target
name to get or show target capabilities.
Export socinfo_get_id_string to get target name.

Change-Id: Ic63b9b3d104981f59a1ac2203ca9d4ddbe73e216
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>