[maguro] Fixes for bluetooth, rild, audio and ducati firmware loading

1) Let the bcm firmware service not stall the boot process
2) Create a symlink to /dev/mmcblk0p9 as rild crashes if the modem is not at it's hardcoded location
3) Remove invalid pulseaudio sink for bluetooth
4) Load RPMSG kernel modules in early boot for the ducati firmware to load
Is this actually better in terms of synchronizedness/stalling than running the binary in the background? Will systemd have a better idea of when this service has been started? Also, `exit 0` is redundant, but you could maybe do `|| exit 1` at the end of the `brcm_patchram_plus` line to detect errors where that utility exits with an error code.