PCI: dwc: Skip PCIE_MSI_INTR0* programming if MSI is disabled

If MSI is disabled, there's no need to program PCIE_MSI_INTR0_MASK
and PCIE_MSI_INTR0_ENABLE registers.

Link: https://lore.kernel.org/r/20201009155436.27e67238@xhacker.debian


Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>