ALSA: aloop: Mark paused device as inactive

Show paused ALSA aloop device as inactive, i.e. the control
"PCM Slave Active" set as false. Notification sent upon state change.

This makes it possible for client capturing from aloop device to know if
data is expected. Without it the client expects data even if playback
is paused.

Signed-off-by: Robert Rosengren <robert.rosengren@axis.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>