ARM: ep93xx: simone: let the mmc_spi driver handle the card detect

This board uses a GPIO for the MMC card detect. Let the mmc_spi
driver handle it instead of the platform code.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>