mmc: make MMC driver entries dependent on MMC

Currently, CONFIG_MMC is not related to any other options by
"depends on" or "select".  One of big advantages of using Kconfig
is automatic dependency tracking, but the current state is lacking
it.  As the first step, make the existing MMC driver entries depend
on MMC.

This commit was created by the following steps:

[1] Run the following script:

--------------------8<--------------------
rm -f tmp.txt

for d in $(find . -path './configs/*_defconfig')
do
        if grep -q -e 'CONFIG_MSM_SDHCI=y' $d ||
           grep -q -e 'CONFIG_ATMEL_SDHCI=y' $d ||
           grep -q -e 'CONFIG_ROCKCHIP_DWMMC=y' $d ||
           grep -q -e 'CONFIG_SH_SDHI=y' $d ||
           grep -q -e 'CONFIG_PIC32_SDHCI=y' $d ||
           grep -q -e 'CONFIG_ZYNQ_SDHCI=y' $d ||
           grep -q -e 'CONFIG_ROCKCHIP_SDHCI=y' $d ||
           grep -q -e 'CONFIG_MMC_UNIPHIER=y' $d ||
           grep -q -e 'CONFIG_SANDBOX_MMC=y' $d
        then
                echo CONFIG_MMC=y >> $d
                echo ${d#./configs/} >> tmp.txt
        fi
done

tools/moveconfig.py -y -s -d tmp.txt
rm tmp.txt
--------------------8<--------------------

[2] surround MMC driver entries with "if MMC" and "endif"

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>