mmc: s5p_sdhci: remove duplicated card detect code

mmc: s5p_sdhci: remove duplicated card detect code

The common sdhci infrastructure is already parsing the cd-gpios
property, since commit 451931ea7002 ("mmc: sdhci: Read cd-gpio from
devicetree"). The s5p code is therefore duplicated, and also broken
since it assumes that the GPIO value is inverted, while the sdhci code
correctly follows the ACTIVE_LOW/ACTIVE_HIGH flag specified in the
device tree.

This fix was originally authored by Simon Shields:
https://github.com/fourkbomb/u-boot/commit/2eac9dea7903

The change has been tested on exynos4210-i9100, a device similar to
exynos4210-trats.

Signed-off-by: Henrik Grimler <henrik@grimler.se>
Reviewed-by: Anand Moon <linux.amoon@gmail.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Peng Fan <peng.fan@nxp.com>