dt-bindings: phy: spacemit: Add SpacemiT PCIe/combo PHY

dt-bindings: phy: spacemit: Add SpacemiT PCIe/combo PHY

Add the Device Tree binding for the PCIe/USB 3.0 combo PHY found in
the SpacemiT K1 SoC.  This is one of three PCIe PHYs, and is unusual
in that only the combo PHY can perform a calibration step needed to
determine settings used by the other two PCIe PHYs.

Calibration must be done with the combo PHY in PCIe mode, and to allow
this to occur independent of the eventual use for the PHY (PCIe or USB)
some PCIe-related properties must be supplied: clocks; resets; and a
syscon phandle.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Alex Elder <elder@riscstar.com>
Link: https://lore.kernel.org/all/ba532f8d-a452-40e5-af46-b58b89f70a92@linaro.org/
Tested-by: Yixun Lan <dlan@gentoo.org>
Link: https://patch.msgid.link/20251218151235.454997-2-elder@riscstar.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>