HP Envy AiO 32-a12xxx has an external amp that is controlled via GPIO
bit 0x04.  However, unlike other devices, this amp seems to shut down
itself after the certain period, hence the OS needs to up/down the bit
dynamically only during the actual playback.

This patch adds the control of the GPIO bit via the existing pcm_hook
mechanism.  Ideally it should be triggered at the actual stream start,
but we have only the state change at prepare/cleanup, so use those for
switching the GPIO bit on/off.  This should be good enough for the
purpose, and was actually confirmed to work fine.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=212873
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210504091802.13200-1-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>