configure: make pulseaudio and alsa configurable options

Allows disabling pulseaudio and alsa support at configure time
making builds more deterministic.

Change-Id: I4f1719cf831458b1d5ad3ebc01f6782b897d392c
Reviewed-by: Martin Jansa <Martin.Jansa@gmail.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Kalle Viironen <kalle.viironen@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>