ANDROID: add tty_schedule_flip() back to the kernel

Commit 2ea77b0b ("tty: drop tty_schedule_flip()") removed
tty_schedule_flip() as all in-kernel users were properly converted over
to use tty_flip_buffer_push(), but this function still needs to be here
for older out-of-tree Android-only drivers to preserve the ABI.

So provide a wrapper function for it to keep them alive for now.

Bug: 161946584
Fixes: 2ea77b0b ("tty: drop tty_schedule_flip()")
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I8893f07cf68bc3502ac6f0f7f0a26b0eec3726a2