mmc: dw_mmc: modify the dt-binding for removing slot-node and supports-highspeed

mmc: dw_mmc: modify the dt-binding for removing slot-node and supports-highspeed

Almost all SoCs use one slot per host controller.
(Even if controller can support the multiple slot, Recommend to use one slot per host controller.)
Don't use the slot-node and deprecate the "supports-highspeed" property.
Instead, use the cap-mmc/sd-highspeed.

Signed-off-by: Jaehoon Chung <[email protected]>
Reviewed-by: Tushar Behera <[email protected]>
Reviewed-by: Ulf Hansson <[email protected]>
Tested-by: Sachin Kamat <[email protected]>
Acked-by: Seungwon Jeon <[email protected]>
Reviewed-by: Doug Anderson <[email protected]>
Signed-off-by: Ulf Hansson <[email protected]>