Include plat/sdhci.h header in the sdhci code to bring the prototypes of
defined functions and fix W=1 compile warnings:

    arch/arm/mach-s3c24xx/setup-sdhci-gpio.c:21:6: warning: no previous prototype for 's3c2416_setup_sdhci0_cfg_gpio' [-Wmissing-prototypes]
    arch/arm/mach-s3c24xx/setup-sdhci-gpio.c:26:6: warning: no previous prototype for 's3c2416_setup_sdhci1_cfg_gpio' [-Wmissing-prototypes]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>