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/mcx_defconfig b/configs/mcx_defconfig
index 767f433..248c18d 100644
--- a/configs/mcx_defconfig
+++ b/configs/mcx_defconfig
@@ -6,6 +6,8 @@
 CONFIG_VIDEO=y
 CONFIG_FIT=y
 CONFIG_BOOTDELAY=3
+# CONFIG_CONSOLE_MUX is not set
+CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="mcx # "