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/BSC9131RDB_NAND_defconfig b/configs/BSC9131RDB_NAND_defconfig
index 46b5b8e..bf26e23 100644
--- a/configs/BSC9131RDB_NAND_defconfig
+++ b/configs/BSC9131RDB_NAND_defconfig
@@ -9,6 +9,7 @@
 CONFIG_OF_STDOUT_VIA_ALIAS=y
 CONFIG_SYS_EXTRA_OPTIONS="BSC9131RDB,NAND"
 CONFIG_BOOTDELAY=10
+CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 # CONFIG_CMD_IMLS is not set