alsa: refactor alsa's device implementation to match device interface

[Trek Hopton]

When the ALSA device was first implemented, we didn’t have a device interface to use for revid input devices. When we moved to implementing a common device interface for revid inputs the ALSA code was modified to work with that interface however it’s not optimal.

• The Set() function of the interface should be implemented and used instead of ALSA’s Setup() function.
• The Paused() function should be done away with and the device should work with calls to Start() and Stop() since that is how revid uses devices.

Note, the device implementation does currently work with revid but it would be simpler and more maintainable if these changes were made.

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