dt-bindings: pci: spacemit: Introduce PCIe host controller

dt-bindings: pci: spacemit: Introduce PCIe host controller

Add the Devicetree binding for the PCIe Root Complex found on the SpacemiT
K1 SoC.  This Root Complex is derived from the Synopsys Designware PCIe IP.
It supports up to three PCIe ports operating at PCIe link speed up to 5
GT/sec. One of the ports uses a combo PHY, which is typically used to
support a USB3 port.

Signed-off-by: Alex Elder <elder@riscstar.com>
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>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20251113214540.2623070-4-elder@riscstar.com