Stream: Add stub

Signed-off-by: Bart Kuivenhoven <bemkuivenhoven@gmail.com>
fs: pipe: Rename stream to pipe

Signed-off-by: Bart Kuivenhoven <bemkuivenhoven@gmail.com>
fs: pipe: Add pipe reference count

Signed-off-by: Bart Kuivenhoven <bemkuivenhoven@gmail.com>