soc: fsl: dpio: add support for irq coalescing per software portal

In DPAA2 based SoCs, the IRQ coalesing support per software portal has 2
configurable parameters:
 - the IRQ timeout period (QBMAN_CINH_SWP_ITPR): how many 256 QBMAN
   cycles need to pass until a dequeue interrupt is asserted.
 - the IRQ threshold (QBMAN_CINH_SWP_DQRR_ITR): how many dequeue
   responses in the DQRR ring would generate an IRQ.

Add support for setting up and querying these IRQ coalescing related
parameters.

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