hexagonrpc for Debian

The systemd service uses a helper script to start hexagonrpcd with the correct
configuration for the device it's running on. You can override those settings
by executing `systemctl edit hexagonrpcd` and setting the following environment
variables, default values in parenthesis: 
- hexagonrpcd_device	(/dev/fastrpc-adsp)
- hexagonrpcd_dsp	(adsp)
- hexagonrpcd_fw_dir	(/var/lib/droid-juicer/sensors/)
- hexagonrpcd_extra	(-s)

The `hexagonrpc_fw_dir` argument is set to the path where droid-juicer extracts
the needed files from the original Android partitions.

Two services are also provided to stop the daemon on suspend and restart it on
resume, some devices (google sargo ...) being known to crash if hexagonrpcd is
active during suspend:
https://gitlab.com/postmarketOS/pmaports/-/merge_requests/5400/

 -- Alexandre Viard <xela@viard.dev>  Wed, 25 Sep 2024 22:42:55 +0200