sparc64: generate data access exception on RW violation

- separate PRIV and PROT handling
- DPRINTF_MMU macro to clean up debug code
- dump mmu_idx, trap level and mmu context registers
  along with address translation values

Signed-off-by: Igor V. Kovalenko <igor.v.kovalenko@gmail.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
