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/at91sam9261ek_dataflash_cs3_defconfig b/configs/at91sam9261ek_dataflash_cs3_defconfig
index 63304f5..f51a145 100644
--- a/configs/at91sam9261ek_dataflash_cs3_defconfig
+++ b/configs/at91sam9261ek_dataflash_cs3_defconfig
@@ -3,6 +3,8 @@
 CONFIG_TARGET_AT91SAM9261EK=y
 CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9261,SYS_USE_DATAFLASH_CS3"
 CONFIG_BOOTDELAY=3
+# CONFIG_CONSOLE_MUX is not set
+CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="U-Boot> "
 # CONFIG_CMD_BDI is not set