ptp: ocp: adjust sysfs entries to expose tty information

Implement additional attribute group to expose serial port information.
Fixes tag points to the commit which introduced the change in serial
port subsystem and made it impossible to use symlinks.

Fixes: b286f4e8 ("serial: core: Move tty and serdev to be children of serial core port device")
Signed-off-by: Vadim Fedorenko <vadfed@meta.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>