PCI: xilinx-nwl: Modify ECAM size to enable support for 256 buses

The PCIe Root Port controller expects ECAM size to be set through software.

As such, update the value of the NWL_ECAM_VALUE_DEFAULT macro to 16 to
allow the controller to address the 256 MB ECAM region and, as such,
enable support for detecting up to 256 buses.

[kwilczynski: commit log]
Link: https://patchwork.kernel.org/project/linux-pci/patch/20231016051102.1180432-5-thippeswamy.havalige@amd.com/


Signed-off-by: Thippeswamy Havalige <thippeswamy.havalige@amd.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>