staging: fsl-mc: Populate the IRQ pool for an MC bus instance

Scan the corresponding DPRC container to get total count
of IRQs needed by all its child DPAA2 objects. Then,
preallocate a set of MSI IRQs with the DPRC's ICID
(GIT-ITS device Id) to populate the the DPRC's IRQ pool.
Each child DPAA2 object in the DPRC and the DPRC object itself
will allocate their necessary MSI IRQs from the DPRC's IRQ pool,
in their driver probe function.

Signed-off-by: J. German Rivera <German.Rivera@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>