serial: etraxfs-uart: Convert to uart_console_device instead of open-coded

The implementation of cris_console_device() is exactly the same as
uart_console_device(), so let's switch to use uart_console_device().

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Niklas Cassel <nks@flawful.org>
Acked-by: Jesper Nilsson <jesper.nilsson@axis.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>