mmc: Add support for enumerating MMC card in a given mode using mmc command

Add support for enumerating MMC card in a given mode using mmc rescan and
mmc dev commands. The speed mode is provided as the last argument in these
commands and is indicated using the index from enum bus_mode in
include/mmc.h. A speed mode can be set only if it has already been enabled
in the device tree.

Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Tested-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index ffef3cc..3a857b3 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -2389,4 +2389,14 @@
 	help
 	  UBIFS is a file system for flash devices which works on top of UBI.
 
+config MMC_SPEED_MODE_SET
+	bool "set speed mode using mmc command"
+	depends on CMD_MMC
+	default n
+	help
+	  Enable setting speed mode using mmc rescan and mmc dev commands.
+	  The speed mode is provided as the last argument in these commands
+	  and is indicated using the index from enum bus_mode in
+	  include/mmc.h. A speed mode can be set only if it has already
+	  been enabled in the device tree.
 endmenu