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/digsy_mtc_defconfig b/configs/digsy_mtc_defconfig
index e3ddb4b..20491a4 100644
--- a/configs/digsy_mtc_defconfig
+++ b/configs/digsy_mtc_defconfig
@@ -4,6 +4,8 @@
 CONFIG_TARGET_DIGSY_MTC=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_BOOTDELAY=1
+# CONFIG_CONSOLE_MUX is not set
+CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_HUSH_PARSER=y
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="autoboot in %d seconds\n"