soc: fsl: dpio: extract the QBMAN clock frequency from the attributes

Through the dpio_get_attributes() firmware call the dpio driver has
access to the QBMAN clock frequency. Extend the structure which holds
the firmware's response so that we can have access to this information.

This will be needed in the next patches which also add support for
interrupt coalescing which needs to be configured based on the
frequency.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>