Cpu provides 16x lanes for direct connection with it for graphics and additional 4x lanes (called DMI 3.0) that are used for chipset. Chipset can provide up to additional 24x lanes, but for how much are used is for manufacturer to decide. But most of time all 1x and 4x slots go into chipset. But see in your manual if there aren't conflicts with pcie ssd as they can render some slots unusable.