firmware: ti_sci: rm: Remove ring_get_config support

The ring_get_cfg (0x1111 message) is not used and it is not supported by
sysfw for a long time.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>