alsa-mixer: add hw_device_index to pa_alsa_mapping

alsa-mixer: add hw_device_index to pa_alsa_mapping

We have so far assumed that HDMI always uses device indexes 3, 7, 8, 9,
10, 11, 12 and 13. These values are hardcoded in the path configuration.
The Intel HDMI LPE driver, however, uses different device numbering
scheme. Since the indexes aren't always the same, we need to query the
hw device index from ALSA.

Later patches will use the queried index for HDMI jack detection and ELD
information reading.

BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=100488