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/mx6dlarm2_lpddr2_defconfig b/configs/mx6dlarm2_lpddr2_defconfig
index c507278..19fede6 100644
--- a/configs/mx6dlarm2_lpddr2_defconfig
+++ b/configs/mx6dlarm2_lpddr2_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_MX6=y
 CONFIG_TARGET_MX6QARM2=y
+# CONFIG_CMD_BMODE is not set
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx6qarm2/imximage_mx6dl.cfg,MX6DL,MX6DL_LPDDR2,DDR_MB=512"
 CONFIG_BOOTDELAY=3
 CONFIG_BOARD_EARLY_INIT_F=y