serial: add static directive to local functions

The functions _serial_putc, _serial_putc_raw, _serial_puts,
_serial_getc, _serial_tstc, _serial_setbrg are defined and used
locally in each of serial_ns16550.c and serial_s3c24x0.c.

Add static directive to them and remove declarations from
include/common.h.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>
3 files changed