serial: Remove duplicated macro definition of port type

There exists the same macro definition of port type from 0 to 13
in include/uapi/linux/serial.h, remove these duplicated code in
include/uapi/linux/serial_core.h which includes the former header.

Acked-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/r/1588853015-28392-1-git-send-email-yangtiezhu@loongson.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>