BL808 RISC-V support

[pauljurczak]

This is a repost of https://community.platformio.org/t/bl808-risc-v-support/30892.

There are new RISC-V boards popping out almost daily with great price/performance ratio, e.g. Sipeed M1s Dock M1s DOCK - Sipeed Wiki, which is using BL808 RISC-V MCU. It is very likely that the BL602/BL604, BL702/BL704/BL706, BL616/BL618, BL808 family supported by bl_mcu_sdk (https://github.com/bouffalolab/bl_mcu_sdk) will be very popular among makers, and it would be great to have PlatformIO support.

[maxgerhardt]

BL602/BL604, BL702/BL704/BL706, BL616/BL618, BL808 family supported by bl_mcu_sdk (https://github.com/bouffalolab/bl_mcu_sdk)

Interesting, if that SDK supports all the chips, we might just have to update the current builder script for it we have in https://github.com/Community-BL-IOT/. We are already able to compile for BL60x and their SDK here.

[ivankravets]

Duplicate of #4046