ALSA: xen-front: Use Xen common shared buffer implementation

Use page directory based shared buffer implementation
now available as common code for Xen frontend drivers.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

ALSA: xen-front: Implement ALSA virtual sound driver

Implement essential initialization of the sound driver:
- introduce required data structures
- handle driver registration
- handle sound card registration
- register sound driver on backend connection
- remove sound driver on backend disconnect

Initialize virtual sound card with streams according to the
Xen store configuration.

Implement ALSA driver operations including:
- manage frontend/backend shared buffers
- manage Xen bus event channel states

Implement requests from front to back for ALSA
PCM operations.
- report ALSA period elapsed event: handle XENSND_EVT_CUR_POS
notifications from the backend when stream position advances
during playback/capture. The event carries a value of how
many octets were played/captured at the time of the event.
- implement explicit stream parameter negotiation between
backend and frontend: handle XENSND_OP_HW_PARAM_QUERY request
to read/update configuration space for the parameter given:
request passes desired parameter interval and the response to
this request returns min/max interval for the parameter to be used.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

ALSA: xen-front: Implement Xen event channel handling

Handle Xen event channels:
- create for all configured streams and publish
corresponding ring references and event channels in Xen store,
so backend can connect
- implement event channels interrupt handlers
- create and destroy event channels with respect to Xen bus state

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

ALSA: xen-front: Read sound driver configuration from Xen store

Read configuration values from Xen store according
to xen/interface/io/sndif.h protocol:
- introduce configuration structures for different
components, e.g. sound card, device, stream
- read PCM HW parameters, e.g rate, format etc.
- detect stream type (capture/playback)
- read device and card parameters

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

ALSA: xen-front: Introduce Xen para-virtualized sound frontend driver

Introduce skeleton of the para-virtualized Xen sound
frontend driver.

Initial handling for Xen bus states: implement
Xen bus state machine for the frontend driver according to
the state diagram and recovery flow from sound para-virtualized
protocol: xen/interface/io/sndif.h.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>