- Use bus_{read,write}_*(9) instead of bus_space_{read,write}_*(9)

- Use bus_{read,write}_*(9) instead of bus_space_{read,write}_*(9)
  in order to get rid of bus space handle and tag in struct sym_hcb.
- Remove unused members related to bus addresses in struct sym_hcb.
- sym(4) takes care of allocating an instance of struct sym_hcb
  itself so don't let newbus allocate it as an unused softc also.
- Add basic MPSAFE locking. This includes changing the sym(4) CCBs
  to be allocated up-front instead of on demand as needed. Besides
  making these allocations more likely to succeed, this also solves
  the problem of calling bus_dmamap_create(9) with the SIM mutex
  held.

Reviewed by:	scottl
MFC after:	1 month