tty: serial: 8250: 8250_port: Move prototypes to shared location

mainline inclusion
from mainline-v5.11-rc1
commit a609c580
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5L672
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a609c58086e381c13bdad1ba97e6510a13d465e7



--------------------------------

Fixes the following W=1 kernel build warning(s):

 drivers/tty/serial/8250/8250_port.c:349:14: warning: no previous prototype for ‘au_serial_in’ [-Wmissing-prototypes]
 drivers/tty/serial/8250/8250_port.c:359:6: warning: no previous prototype for ‘au_serial_out’ [-Wmissing-prototypes]

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Mike Hudson <Exoray@isys.ca>
Cc: linux-serial@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201112105857.2078977-3-lee.jones@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yi Yang <yiyang13@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: Wang Weiyang <wangweiyang2@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>