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/usbarmory_defconfig b/configs/usbarmory_defconfig
index ed16105..4325617 100644
--- a/configs/usbarmory_defconfig
+++ b/configs/usbarmory_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_MX5=y
 CONFIG_TARGET_USBARMORY=y
+# CONFIG_CMD_BMODE is not set
 CONFIG_DISTRO_DEFAULTS=y
 # CONFIG_CMD_IMLS is not set
 CONFIG_CMD_MEMTEST=y