Adding new chipset to the PlatformIO

Do you mean the 8-bit 8051 controller series? That’s the only type where PlatformIO has support for these chips as of now. E.g. this one.

Generally explained in Custom Platform & Board — PlatformIO latest documentation with some specific questions explained in Adding a new board to PlatformIO - #6 by snovotill.

If you say which exact chip you mean you might get better help.