sh: ecovec24: Remove MMCIF and SDHI .set_pwr() callbacks

The MMCIF and SHDI platform data .set_pwr() callbacks are used to
control the vmmc/vqmmc power supplies. As the power supplies already
register control GPIOs there's no need to perform the operation
manually. Remove the callback functions.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>