dt-bindings: phy: rockchip: add RK3588 PCIe v3 phy

When the RK3568 PCIe v3 PHY supported has been upstreamed, RK3588
support was included, but the DT binding does not reflect this.
This adds the missing bits.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20230717173512.65169-2-sebastian.reichel@collabora.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>