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>

board/hisilicon/hikey/hikey.c

@@ -347,7 +347,7 @@ static int init_dwmmc(void)
 {
 	int ret;
 
-#ifdef CONFIG_DWMMC
+#ifdef CONFIG_MMC_DW
 
 	/* mmc0 clocks are already configured by ATF */
 	ret = hi6220_pinmux_config(PERIPH_ID_SDMMC0);

board/samsung/common/board.c

@@ -260,7 +260,7 @@ static int init_mmc(void)
 
 static int init_dwmmc(void)
 {
-#ifdef CONFIG_DWMMC
+#ifdef CONFIG_MMC_DW
 	return exynos_dwmmc_init(gd->fdt_blob);
 #else
 	return 0;