PCI: dwc: Remove old MSI IRQs API

Remove the unused old MSI IRQs API from pcie-designware based on
struct msi_controller that should now be considered obsolete.

Signed-off-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Tested-by: Niklas Cassel <niklas.cassel@axis.com>
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>