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/warp7_defconfig b/configs/warp7_defconfig
index b5489b0..db1c7cb 100644
--- a/configs/warp7_defconfig
+++ b/configs/warp7_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_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/warp7/imximage.cfg"
 CONFIG_HUSH_PARSER=y
 # CONFIG_CMD_BOOTD is not set