PCI: intel-gw: Fix INTx enable

PCI: intel-gw: Fix INTx enable

The legacy PCI interrupt lines need to be enabled using PCIE_APP_IRNEN bits
13 (INTA), 14 (INTB), 15 (INTC) and 16 (INTD). The old code however was
taking (for example) "13" as raw value instead of taking BIT(13).  Define
the legacy PCI interrupt bits using the BIT() macro and then use these in
PCIE_APP_IRN_INT.

Link: https://lore.kernel.org/r/20210106135540.48420-1-martin.blumenstingl@googlemail.com
Fixes: e4af7edf56a9 ("PCI: dwc: intel: PCIe RC controller driver")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rahul Tanwar <rtanwar@maxlinear.com>