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/sniper_defconfig b/configs/sniper_defconfig
index a44082e..02b51c4 100644
--- a/configs/sniper_defconfig
+++ b/configs/sniper_defconfig
@@ -3,6 +3,7 @@
 # CONFIG_SPL_EXT_SUPPORT is not set
 # CONFIG_SPL_NAND_SUPPORT is not set
 CONFIG_TARGET_SNIPER=y
+CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="sniper # "