mmc: move DesignWare-based drivers to Kconfig

Move (and rename) the following CONFIG options to Kconfig:

  CONFIG_EXYNOS_DWMMC  (renamed to CONFIG_MMC_DW_EXYNOS)
  CONFIG_HIKEY_DWMMC   (renamed to CONFIG_MMC_DW_K3)
  CONFIG_SOCFPGA_DWMMC (renamed to CONFIG_MMC_DW_SOCFPGA)

The "HIKEY" is a board name, so it is not suitable for the MMC
controller name.  I am following the name used in Linux.

This commit was generated as follows:

[1] Rename the config options with the following command:
find . -name .git -prune -o ! -path ./scripts/config_whitelist.txt \
-type f -print | xargs sed -i -e '
s/CONFIG_EXYNOS_DWMMC/CONFIG_MMC_DW_EXYNOS/g
s/CONFIG_HIKEY_DWMMC/CONFIG_MMC_DW_K3/g
s/CONFIG_SOCFPGA_DWMMC/CONFIG_MMC_DW_SOCFPGA/g
'

[2] Commit the changes

[3] Create the entries in drivers/mmc/Kconfig
    (with default y for EXYNOS and SOCFPGA)

[4] Run the following:
tools/moveconfig.py -y -r HEAD MMC_DW_EXYNOS MMC_DW_K3 MMC_DW_SOCFPGA

[5] Sort and align drivers/mmc/Makefile for readability

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

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