PCI: dwc: Add iATU regions size detection procedure

PCI: dwc: Add iATU regions size detection procedure

The DWC PCIe RC/EP/DM IP core configuration parameters determine the number
of inbound and outbound iATU windows, alignment requirements (which is also
the minimum window size), minimum and maximum sizes.  If internal ATU is
enabled, the former settings are determined by CX_ATU_MIN_REGION_SIZE; the
latter are determined by CX_ATU_MAX_REGION_SIZE.

Determine the required alignment and maximum size supported by the
controller and log it to help verify whether the requested inbound or
outbound memory mappings can be fully created.

Note 1. The extended iATU regions have been supported since DWC PCIe
v4.60a. There is no need in testing the upper limit register availability
for the older cores.

Note 2. The regions alignment is determined with using the fls() method
since the lower four bits of the ATU Limit register can be occupied with
the Circular Buffer Increment setting, which can be initialized with zeros.

Link: https://lore.kernel.org/r/20220624143947.8991-13-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>