Add support for BouffaloLab BL602/BL604

[normanr]

It would be nice to be able to use this library on with bl602 boards (eg: pinecone or newer magichome boards). There is some beginnings of platform-io support for this platform (platformio/platformio-core#4046), and I think this would be required for Tasmota to build for bl602 (ref: arendst/Tasmota#9914).

As I anticipate multiple PRs may be required to get this working, I'm opening this issue to track the implementation.

[crankyoldgit]

Once this board gets more supported (arduino/platformio etc) hopefully it should be a non-herculean effort to add support.
Most of the effort will be in timers, & and interrupt routines. When that is well documented/supported etc in Arduino-land, that is when we could begin to think of add support for it.

Note however, I have no plans as yet to add support or to get the hardware device at present, nor any pressing need.

That said, I won't say no to PRs for it. ;-)