PCI: spacemit: Add SpacemiT PCIe host driver

PCI: spacemit: Add SpacemiT PCIe host driver

Introduce a driver for the PCIe host controller found in the SpacemiT K1
SoC. The hardware is derived from the Synopsys DesignWare PCIe IP. The
driver supports up to three PCIe ports operating at PCIe link speed up to
5 GT/s. The first port uses a combo PHY, which may be configured for use
for USB3 instead.

Signed-off-by: Alex Elder <elder@riscstar.com>
[mani: added FIXME to the comment on disabling ASPM L1]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Tested-by: Jason Montleon <jmontleo@redhat.com>
Tested-by: Johannes Erdfelt <johannes@erdfelt.com>
Tested-by: Aurelien Jarno <aurelien@aurel32.net>
Link: https://patch.msgid.link/20251113214540.2623070-6-elder@riscstar.com