Tegra124 has 4 MMC controllers just like previous versions of the SoC.
Note that there are some non-backwards-compatible HW differences, and
hence a new DT compatible value must be used to describe the HW.

Also enable the relevant controllers in the Venice2 board DT.

power-gpios property suggested by Thierry Reding.
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Tested-by: Thierry Reding <treding@nvidia.com>