src: Add changes for SPI Bluetooth support.

[peterharperuk]

See CYW43_ENABLE_BLUETOOTH. New firmware added that supports Wifi and BT. Firmware now stored as binary data in header files.

[dpgeorge]

I've now merged this with the following minor changes (which were force pushed to this PR branch):

• tweaked comments for new hci functions (changed "bt hci" to "Bluetooth HCI layer")
• removed assert(false) from cyw43_ll_sdpcm_poll_device(), and assert(ret == 0) from cyw43_write_backplane_mem()
• changed CYW43_PRINTF to CYW43_WARN in cyw43_write_backplane_mem()

Also in a follow-up commit I converted the remaining combined binary blob (for the Murata 1DX) to a header file.

[peterharperuk]

Thanks!

[Dirbaio]

:eyes: did you forget to add cyw43_btbus.c? or does something else provide the cyw43_btbus_init etc implementation, like pico-sdk?

[peterharperuk]

Yes. It'll be in the pico-sdk for the time being.