bindings: soc: ti: add documentation for k3 ringacc

The Ring Accelerator (RINGACC or RA) provides hardware acceleration to
enable straightforward passing of work between a producer and a consumer.
There is one RINGACC module per NAVSS on TI AM65x and j721e.

This patch introduces RINGACC device tree bindings.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Tested-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>