PCI: dwc: Add Root Port and Endpoint controller eDMA engine support

Since the DW eDMA core now supports eDMA controllers embedded in locally
accessible DW PCIe Root Ports and Endpoints, register these controllers
when possible.

To do that the DW PCIe core driver needs to perform some preparations
first. First of all, it needs to find the eDMA controller CSRs base
address, whether they are accessible over the Port Logic or iATU unrolled
space.  Afterwards it can try to auto-detect the eDMA controller
availability and number of read/write channels.  If none are found the
procedure silently returns without error.

Secondly, the platform is supposed to provide either combined or
per-channel IRQ signals.  If no valid IRQs set is found, the procedure
returns without error to be backward compatible with platforms where DW
PCIe controllers have eDMA but lack the IRQ description.

Finally, before actually probing the eDMA device we need to allocate LLP
items buffers. After that the DW eDMA can be registered. If registration is
successful, a message regarding the number of detected Read/Write eDMA
channels will be printed to the system as is done for the iATU settings.

Note: the DW PCI controller driver (either host or endpoint mode) is
currently always built-in, so if the DW eDMA core is built as a module
(CONFIG_DW_EDMA=m), eDMA controllers will not be registered even if the
dw-edma module is later loaded.

Link: https://lore.kernel.org/r/20230113171409.30470-28-Sergey.Semin@baikalelectronics.ru


Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Vinod Koul <vkoul@kernel.org>