PCI: mobiveil: Collect the interrupt related operations into a function

Collect the interrupt initialization related operations into
a new function to make code more readable.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Andrew Murray <amurray@thegoodpenguin.co.uk>