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/pxm2_defconfig b/configs/pxm2_defconfig
index ffdfcfe..0f8168f 100644
--- a/configs/pxm2_defconfig
+++ b/configs/pxm2_defconfig
@@ -18,6 +18,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="am335x-pxm50"
 CONFIG_FIT=y
 CONFIG_BOOTDELAY=3
+# CONFIG_CONSOLE_MUX is not set
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SPL=y