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/T1042RDB_PI_SPIFLASH_defconfig b/configs/T1042RDB_PI_SPIFLASH_defconfig
index b241fbd..4d9509c 100644
--- a/configs/T1042RDB_PI_SPIFLASH_defconfig
+++ b/configs/T1042RDB_PI_SPIFLASH_defconfig
@@ -17,6 +17,8 @@
 CONFIG_SYS_EXTRA_OPTIONS="PPC_T1042,T1042RDB_PI,RAMBOOT_PBL,SPL_FSL_PBL,SPIFLASH"
 CONFIG_BOOTDELAY=10
 CONFIG_SILENT_CONSOLE=y
+# CONFIG_CONSOLE_MUX is not set
+CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SPL=y
 CONFIG_SPL_MPC8XXX_INIT_DDR_SUPPORT=y
 CONFIG_HUSH_PARSER=y