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/evb-rk3288_defconfig b/configs/evb-rk3288_defconfig
index f5525db..fd8afe7 100644
--- a/configs/evb-rk3288_defconfig
+++ b/configs/evb-rk3288_defconfig
@@ -5,8 +5,9 @@
 CONFIG_TARGET_EVB_RK3288=y
 CONFIG_SPL_STACK_R_ADDR=0x80000
 CONFIG_DEFAULT_DEVICE_TREE="rk3288-evb"
-# CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_SILENT_CONSOLE=y
+CONFIG_CONSOLE_MUX=y
+# CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_SPL_STACK_R=y
 CONFIG_SPL_STACK_R_MALLOC_SIMPLE_LEN=0x2000
 CONFIG_HUSH_PARSER=y