MIPS: Netlogic: MSI enable fix for XLS

MIPS: Netlogic: MSI enable fix for XLS

MSI interrupts do not work on XLS after commit a776c49
( "PCI: msi: Disable msi interrupts when we initialize a pci device" )
because the change disables MSI interrupts on the XLS PCIe bridges
during the PCI enumeration.

Fix this by enabling MSI interrupts on the bridge in the
arch_setup_msi_irq() function. A new function xls_get_pcie_link()
has been introduced to get the PCI device corresponding to the
top level PCIe bridge on which MSI has to be enabled.

Also, update get_irq_vector() to use the new xls_get_pcie_link()
function and PCI_SLOT() macro for determining the IRQ of PCI devices.

Signed-off-by: Ganesan Ramalingam <ganesanr@broadcom.com>
Signed-off-by: Jayachandran C <jayachandranc@netlogicmicro.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3753/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>