alsa: Find supported samplerates during device scan

alsa: Find supported samplerates during device scan

Since we are using the 'hw' interface of ALSA, we don't have the luxury of
samplerate conversion, given by the 'plughw' interface. If we try to set a
samplerate that is not supported, ALSA will just throw an error.

We can test for the supported samplerates, and create a list of supported
samplerates, then limit the selection to only those values. The frontend can
query the list of supported samplerates.

Signed-off-by: Alexandru Gagniuc <redacted>