pcie: Support PCIe Gen5/Gen6 link speeds

pcie: Support PCIe Gen5/Gen6 link speeds

This patch extends the PCIe link speed option so that slots can be
configured as supporting 32GT/s (Gen5) or 64GT/s (Gen5) speeds.
This is as simple as setting the appropriate bit in LnkCap2 and
the appropriate value in LnkCap and LnkCtl2.

Signed-off-by: Lukas Stockner <lstockner@genesiscloud.com>
Message-Id: <20240215012326.3272366-1-lstockner@genesiscloud.com>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>