Convert CONFIG_CMD_BMODE to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_BMODE

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Make this default y and depend on mx5/6/7]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/mx7dsabresd_defconfig b/configs/mx7dsabresd_defconfig
index 9541e12..9cca305 100644
--- a/configs/mx7dsabresd_defconfig
+++ b/configs/mx7dsabresd_defconfig
@@ -4,6 +4,7 @@
 # CONFIG_ARMV7_VIRT is not set
 CONFIG_IMX_RDC=y
 CONFIG_IMX_BOOTAUX=y
+# CONFIG_CMD_BMODE is not set
 CONFIG_VIDEO=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx7dsabresd/imximage.cfg"
 CONFIG_BOOTDELAY=3