PCI: layerscape: Add the bar_fixed_64bit property to the endpoint driver

The layerscape PCIe controller have 4 BARs.

 BAR0 and BAR1 are 32bit, BAR2 and BAR4 are 64bit and that's a
fixed hardware configuration.

Set the bar_fixed_64bit variable accordingly.

Signed-off-by: Xiaowei Bao <xiaowei.bao@nxp.com>
[lorenzo.pieralisi@arm.com: commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>