mmc: move CONFIG_GENERIC_MMC to Kconfig

Now, CONFIG_GENERIC_MMC seems equivalent to CONFIG_MMC.

Let's create an entry for "config GENERIC_MMC" with "default MMC",
then convert all macro defines in headers to Kconfig.  Almost all
of the defines will go away.

I see only two exceptions:
  configs/blanche_defconfig
  configs/sandbox_noblk_defconfig

They define CONFIG_GENERIC_MMC, but not CONFIG_MMC.  Something
might be wrong with these two boards, so should be checked later.

Anyway, this is the output of the moveconfig tool.

This commit was created as follows:

[1] create a config entry in drivers/mmc/Kconfig

[2] tools/moveconfig.py -r HEAD GENERIC_MMC

[3] manual clean-up of garbage comments in doc/README.* and
    include/configs/*.h

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