Convert CONFIG_SYS_CONSOLE_IS_IN_ENV and CONFIG_CONSOLE_MUX to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_CONSOLE_IS_IN_ENV
   CONFIG_CONSOLE_MUX

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Re-order, re-migrate]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/brxre1_defconfig b/configs/brxre1_defconfig
index 36d980c..90c83b5 100644
--- a/configs/brxre1_defconfig
+++ b/configs/brxre1_defconfig
@@ -10,6 +10,8 @@
 CONFIG_SPL_YMODEM_SUPPORT=y
 CONFIG_SYS_EXTRA_OPTIONS="SERIAL1,CONS_INDEX=1"
 CONFIG_BOOTDELAY=-2
+# CONFIG_CONSOLE_MUX is not set
+CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_VERSION_VARIABLE=y
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set