banking: lay the groundwork

banking: lay the groundwork

Unfortunately the current m6809 gcc build banking support is broken and
doesn't remember to add the bank names with the .db for the bank so it fails
to assemble.

Uglies:
- We put all syscalls in the same bank to avoid having to have a 'far' pointer
  form for the syscall table
- We don't do this for devices, so will need to rig up some far pointer
  hackery for this