arm: toradex: Convert CONFIG_CONSOLE_MUX to Kconfig
This converts the following to Kconfig:
CONFIG_CONSOLE_MUX
Cc: Igor Opaniuk <igor.opaniuk@toradex.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@toradex.com>