common: console: Fix print complete stdio device list

In case CONSOLE_MUX and SYS_CONSOLE_IS_IN_ENV are on and
stdin or stdout or stderr are missing in environment, as fallback, get
these either from stdio_devices[std] or stdio_devices[std]->name.

Fixes: 6b343ab3 ("console: Print out complete stdio device list")

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>