Draft: libssc support

This MR adds support for the Qualcomm Snapdragon Sensor Core (SSC) through the libssc library. Libssc provides all the necessary drivers and glue to interact with the SLPI DSP running on Qualcomm SoCs, iio-sensor-proxy has simple drivers pass through their methods to libssc. The repository of libssc lives on Codeberg.

This MR was already tested for several months in postmarketOS on several SDM845 devices like Oneplus 6/6T, Xiaomi POCOPHONE F1, and SHIFTPHONES SHIFT6mq. Recently, mainline kernels running on newer SoCs like in Fairphones or Xiaomi are also making use of this MR with libssc to make their sensors work.