Switch from rk3399-bluetooth service to btbcm for loading firmware/patchram in dev/current
Current situation is that `brcm_patchram_plus_rk3399` run by `rk3399-bluetooth`:
does not work for ROCK Pi 4b (the /dev/ttyS0 device is already claimed by btbcm module);
is configured to load wrong patchram file for some boards (NanoP*4, OrangePi RK3399 and Firefly RK3399);
It should be deprecated in favour of `btbcm` loading the patchram itself based on the recognised module (it will need some patching for legacy kernels it will be left intact for legacy kernels).
I kept it unmerged as I did not want to trickle last minute changes to v20.08 but this one is pretty safe anyway.
Did I merge it too soon?