greybus: audio: Add Audio Manager

greybus: audio: Add Audio Manager

This is a simple module that keeps a list of connected GB audio
modules.

Whenever a device is attached, an appropriate uevent is sent to
userspace:

    UDEV  [4941.803215] add      /kernel/gb_audio_manager/0 (gb_audio_manager)
    ACTION=add
    CPORT=99
    DEVICES=0x10
    DEVPATH=/kernel/gb_audio_manager/0
    NAME=naim
    PID=64
    SEQNUM=1828
    SLOT=2
    SUBSYSTEM=gb_audio_manager
    USEC_INITIALIZED=802416
    VID=128

And whenever removed:

    UDEV  [4941.836588] remove   /kernel/gb_audio_manager/0 (gb_audio_manager)
    ACTION=remove
    DEVPATH=/kernel/gb_audio_manager/0
    SEQNUM=1833
    SUBSYSTEM=gb_audio_manager
    USEC_INITIALIZED=835681

The API consists of functions for adding, removing and inspecting
added device module descriptions (struct gb_audio_module):

    int                         gb_audio_manager_add(struct gb_audio_module_descriptor *desc);
    int                         gb_audio_manager_remove(int id);
    int                         gb_audio_manager_remove_all(void);
    struct  gb_audio_module*    gb_audio_manager_get_module(int id);
    void                        gb_audio_manager_put_module(struct gb_audio_module *module);
    int                         gb_audio_manager_dump_module(int id);
    void                        gb_audio_manager_dump_all(void);

Devices can be inspected through sysfs in /sys/kernel/gb_audio_manager/{id}/*

If GB_AUDIO_MANAGER_SYSFS is exported as 'true', managing devices can be done
via the SYSFS as well. For instance:

    echo name=naim slot=2 vid=128 pid=64 cport=99 devices=0x10 > /sys/kernel/gb_audio_manager/add
    echo all > /sys/kernel/gb_audio_manager/dump
    echo 2 > /sys/kernel/gb_audio_manager/dump
    echo 2 > /sys/kernel/gb_audio_manager/remove

Signed-off-by: Svetlin Ankov <ankov_svetlin@projectara.com>
Signed-off-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>