PCI: dwc: Add Baikal-T1 PCIe controller support

PCI: dwc: Add Baikal-T1 PCIe controller support

Baikal-T1 SoC is equipped with DWC PCIe v4.60a host controller. It can be
trained to work up to Gen.3 speed over up to x4 lanes. The host controller
is attached to the DW PCIe 3.0 PCS via the PIPE-4 interface, which in its
turn is connected to the DWC 10G PHY. The whole system is supposed to be
fed up with four clock sources: DBI peripheral clock, AXI application
clocks and external PHY/core reference clock generating the 100MHz signal.
In addition to that the platform provide a way to reset each part of the
controller: sticky/non-sticky bits, host controller core, PIPE interface,
PCS/PHY and Hot/Power reset signal. The driver also provides a way to
handle the GPIO-based PERST# signal.

Note due to the Baikal-T1 MMIO peculiarity we have to implement the DBI
interface accessors which make sure the IO operations are dword-aligned.

Link: https://lore.kernel.org/r/20221113191301.5526-21-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>