* support for a subset of the bootrom functions added: fast bit count/ manipulation functions (tested), fast bulk memory fill/ copy functions (tested), flash access functions (NOT tested), debugging support functions (not implemented), miscellaneous functions (not implemented).
* added support for erasing and programming flash from user code. between the first and last call in a programming sequence, the SSI is not in a state where it can handle XIP accesses, so the code that calls the intervening functions must be located in SRAM. this is why I added the time_critical section to rp2040.ld (maybe one should create a dedicated section in ram that is rwx and keep data rwNx).
* flash_program.zig example added
David Sugar