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: Stefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Cc: Dirk Eibach <eibach@gdsys.de>
diff --git a/tools/kwbimage.c b/tools/kwbimage.c
index 1ff17ca..91e0990 100644
--- a/tools/kwbimage.c
+++ b/tools/kwbimage.c
@@ -115,6 +115,7 @@
 	{ 0x78, "sata" },
 	{ 0x9C, "pex"  },
 	{ 0x69, "uart" },
+	{ 0xAE, "sdio" },
 	{},
 };