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/vining_2000_defconfig b/configs/vining_2000_defconfig
index 612292c..0099cab 100644
--- a/configs/vining_2000_defconfig
+++ b/configs/vining_2000_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_MX6=y
 CONFIG_TARGET_SAMTEC_VINING_2000=y
+# CONFIG_CMD_BMODE is not set
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/samtec/vining_2000/imximage.cfg"
 CONFIG_BOOTDELAY=0
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y