ARM: dts: keystone: add interrupt property to PCI controller bindings

Now that Keystone PCIe controller supports error interrupt handling
add interrupt property to PCI controller DT bindings to enable
error interrupt handling.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>