tty: move the async flags from the serial code into the tty includes

These are used with the tty_port flags which are tty generic so move the
flags into a more sensible place. This then makes it possible to add
helpers such as those suggested by Huang Shijie.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index e9f560a..c57e064 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -369,6 +369,7 @@
 header-y += tipc_config.h
 header-y += toshiba.h
 header-y += tty.h
+header-y += tty_flags.h
 header-y += types.h
 header-y += udf_fs_i.h
 header-y += udp.h