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>
diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
index e1f8f9d..44f58b4 100644
--- a/drivers/mmc/Kconfig
+++ b/drivers/mmc/Kconfig
@@ -68,9 +68,17 @@
 	  It is compliant with the SD Host Controller Standard V3.0
 	  specification.
 
+config MMC_DW
+	bool "Synopsys DesignWare Memory Card Interface"
+	help
+	  This selects support for the Synopsys DesignWare Mobile Storage IP
+	  block, this provides host support for SD and MMC interfaces, in both
+	  PIO, internal DMA mode and external DMA mode.
+
 config MMC_DW_ROCKCHIP
 	bool "Rockchip SD/MMC controller support"
 	depends on DM_MMC && OF_CONTROL
+	depends on MMC_DW
 	help
 	  This enables support for the Rockchip SD/MMM controller, which is
 	  based on Designware IP. The device is compatible with at least