tty/serial: use uart_console_write in the RISC-V SBL early console

This enables proper NLCR processing.

Suggested-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Andreas Schwab <schwab@suse.de>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>