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/mccmon6_sd_defconfig b/configs/mccmon6_sd_defconfig
index d478fbe..332eddf 100644
--- a/configs/mccmon6_sd_defconfig
+++ b/configs/mccmon6_sd_defconfig
@@ -5,6 +5,7 @@
 CONFIG_TARGET_MCCMON6=y
 CONFIG_SPL_MMC_SUPPORT=y
 CONFIG_SPL_SERIAL_SUPPORT=y
+# CONFIG_CMD_BMODE is not set
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/liebherr/mccmon6/mon6_imximage_sd.cfg,MX6QDL"
 CONFIG_SPL=y
 CONFIG_SPL_ENV_SUPPORT=y