PCI: dwc: Move forward the iATU detection process

In the dw_pcie_ep_init(), it depends on the detected iATU region
numbers to allocate the in/outbound window management bit map.
It fails after the commit 281f1f99 ("PCI: dwc: Detect number
of iATU windows").

So this patch move the iATU region detection into a new function,
move forward the detection to the very beginning of functions
dw_pcie_host_init() and dw_pcie_ep_init(). And also remove it
from the dw_pcie_setup(), since it's more like a software
perspective initialization step than hardware setup.

Fixes: 281f1f99 ("PCI: dwc: Detect number of iATU windows")
Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>