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/ts4800_defconfig b/configs/ts4800_defconfig
index 5a4bf27..4d4aebd 100644
--- a/configs/ts4800_defconfig
+++ b/configs/ts4800_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_MX5=y
 CONFIG_TARGET_TS4800=y
+# CONFIG_CMD_BMODE is not set
 CONFIG_BOOTDELAY=1
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y