kwbimage: Add support for SDIO/MMC boot device selection

This patch adds support to select the "sdio" as boot device in the
kwbimage.cfg file. This line selects this SDIO device:

BOOT_FROM  sdio

Tested on Marvell DB-88F6820-GP board.
Signed-off-by: NStefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Cc: Dirk Eibach <eibach@gdsys.de>

tools/kwbimage.c

@@ -115,6 +115,7 @@ struct boot_mode boot_modes[] = {
 	{ 0x78, "sata" },
 	{ 0x9C, "pex"  },
 	{ 0x69, "uart" },
+	{ 0xAE, "sdio" },
 	{},
 };