mmc: move CONFIG_DWMMC to Kconfig, renaming to CONFIG_MMC_DW

This commit was created as follows:

[1] Rename the option with the following command:
find . -name .git -prune -o ! -path ./scripts/config_whitelist.txt \
-type f -print | xargs sed -i -e 's/CONFIG_DWMMC/CONFIG_MMC_DW/g'

[2] create the entry for MMC_DW in drivers/mmc/Kconfig
    (the prompt and help were copied from Linux)

[3] run "tools/moveconfig.py -y MMC_DW"

[4] add "depends on MMC_DW" to the MMC_DW_ROCKCHIP entry

[5] Clean-up doc/README.socfpga by hand

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Marek Vasut <marex@denx.de>

doc/README.socfpga

@@ -20,8 +20,5 @@ controller support within SOCFPGA
 #define CONFIG_SYS_MMC_MAX_BLK_COUNT	256
 -> Using smaller max blk cnt to avoid flooding the limited stack in OCRAM
 
-#define CONFIG_DWMMC
--> Enable the common DesignWare SDMMC controller framework
-
 #define CONFIG_SOCFPGA_DWMMC
 -> Enable the SOCFPGA specific driver for DesignWare SDMMC controller