ext/alsa/: Clean up and simplify alsa device probing. Make it actually work for multiple classes. Don't cache results...

Original commit message from CVS:
* ext/alsa/gstalsadeviceprobe.c: (gst_alsa_get_device_list),
(gst_alsa_device_property_probe_probe_property),
(gst_alsa_device_property_probe_needs_probe),
(gst_alsa_device_property_probe_get_values),
(gst_alsa_type_add_device_property_probe_interface):
* ext/alsa/gstalsadeviceprobe.h:
* ext/alsa/gstalsamixerelement.c:
(gst_alsa_mixer_element_init_interfaces):
* ext/alsa/gstalsamixerelement.h:
Clean up and simplify alsa device probing. Make it actually work
for multiple classes. Don't cache results any longer.
* ext/alsa/gstalsasink.c: (gst_alsasink_init_interfaces),
(gst_alsasink_init):
* ext/alsa/gstalsasrc.c: (gst_alsasrc_dispose),
(gst_alsasrc_interface_supported), (gst_implements_interface_init),
(gst_alsasrc_init_interfaces), (gst_alsasrc_set_property):
Make alsasink and alsasrc implement the GstPropertyProbe interface
for device probing (#342181).
Patch by: Martin Szulecki  <gnomebugzilla at sukimashita com>