Complete refactor of FDISK

[lydon42]

FDISK needs to use the fixed QSPI interface, as introduced in new MEGAFLASH.

So we possibly need to:

• separate M65 build from PC build
• use mega65-libc for common functions
• make QSPI flash some sort of library
• rewrite fdisk to use that (making it also more compatible with non mega65 PCB platforms)
• possibly also change to using mhexes instead of what is now used for screen output
  • this could mean that we make qspi, nohysdc, and mhexes into libraries so that we can use those for all the tools