uboot-imx

console: Don't enable CONFIG-CONSOLE_MUX, etc. in SPL

CONFIG_CONSOLE_MUX and CONFIG_SYS_CONSOLE_IS_IN_ENV are not applicable
for SPL. Update the console code to use CONFIG_IS_ENABLED(), so that these
options will be inactive in SPL.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>