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/plutux_defconfig b/configs/plutux_defconfig
index 3885adb..0d3ffaa 100644
--- a/configs/plutux_defconfig
+++ b/configs/plutux_defconfig
@@ -5,6 +5,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="tegra20-plutux"
 CONFIG_FIT=y
 CONFIG_OF_SYSTEM_SETUP=y
+CONFIG_CONSOLE_MUX=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="Tegra20 (Plutux) # "
 CONFIG_CMD_BOOTZ=y