pci: xilinx: Enable MMIO region

The host bridge MMIO region is disabled by default due to which MMIO
accesses cause an exception. Fix it by setting the bridge enable bit.
This change is ported from the linux pcie-xilinx driver.

Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Reviewed-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/20231116165103.140968-3-mchitale@ventanamicro.com


Signed-off-by: Michal Simek <michal.simek@amd.com>