PCE PCE-322A support

libsigrok now supports the PCE PCE-322A sound level meter.

This is a USB-based sound level meter with various settings such frequency weighting (A or C), a frequency range of 31.5 Hz to 8 kHz, an internal memory store, an built-in RTC, and others.

The device protocol is documented in the sigrok wiki, as usual.

The driver was contributed by George Hopkins, thanks a lot!