dmaengine: dw-edma: Add mem-mapped LL-entries support

dmaengine: dw-edma: Add mem-mapped LL-entries support

Currently the DW eDMA driver only supports the linked lists memory
allocated locally with respect to the remote eDMA engine setup. It means
the linked lists will be accessible by the CPU via the MMIO space only. If
eDMA is embedded into the DW PCIe Root Ports or local Endpoints (which
support will be added in subsequent commits) the linked lists are supposed
to be allocated in the CPU memory. In that case the LL-entries can be
directly accessed, while the former case implies using the MMIO accessors
for that.

In order to have both cases supported by the driver, the dw_edma_region
descriptor should be fixed to contain the MMIO-backed and just memory-based
virtual addresses. The linked lists initialization procedure will use one
of them depending on the eDMA device nature. If the eDMA engine is embedded
into the local DW PCIe Root Port/Endpoint controllers, the list entries
will be directly accessed by referencing the corresponding structure
fields.  Otherwise the MMIO accessors usage will be preserved.

Link: https://lore.kernel.org/r/20230113171409.30470-24-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>
Acked-by: Vinod Koul <vkoul@kernel.org>