uboot-imx

rockchip: Disable sdio mmc slot on rk3288-firefly

U-Boot can't use the sdio card so turn it of to prevent things getting
confused/struck when trying to use the card as storage.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>