mmc: complete unfinished move of CONFIG_MMC

Commit 7a777f6d6f35 ("mmc: Add generic Kconfig option") created
a Kconfig entry for this option without any actual moves, then
commit 44c798799f66 ("sunxi: Use Kconfig CONFIG_MMC") moved
instances only for SUNXI.

We generally do not like such partial moves.  This kind of work
is automated by tools/moveconfig.py, so it is pretty easy to
complete this move.

I am adding "default ARM || PPC || SANDBOX" (suggested by Tom).
This shortens the configs and will ease new board porting.

This commit was created as follows:

[1] Edit Kconfig (remove the "depends on", add the "default",
    copy the prompt and help message from Linux)

[2] Run 'tools/moveconfig.py -y -s -r HEAD MMC'

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/configs/netspace_v2_defconfig b/configs/netspace_v2_defconfig
index b8ccecd..5b5954b 100644
--- a/configs/netspace_v2_defconfig
+++ b/configs/netspace_v2_defconfig
@@ -2,6 +2,7 @@
 CONFIG_KIRKWOOD=y
 CONFIG_TARGET_NETSPACE_V2=y
 CONFIG_IDENT_STRING=" NS v2"
+# CONFIG_MMC is not set
 CONFIG_SYS_EXTRA_OPTIONS="NETSPACE_V2"
 CONFIG_BOOTDELAY=3
 CONFIG_CONSOLE_MUX=y