base-defaults: Add PulseAudio daemon.conf.d snippet to change default sample rate
This fixes call audio on the devkit. The stock default sample rate is 44.1 kHz and PulseAudio wants a multiple of 8 kHz due to Haegtesse. Confusion ensues because the hardware restricts the available sample rate in either the ADC or DAC once the other side is opened. PulseAudio assumes that the list of available sample rates never changes. We work around this by making the default sample rate 48 kHz, a multiple of 8 kHz.