target-xtensa: implement memory protection options

- TLB opcode group;
- region protection option (ISA, 4.6.3);
- region translation option (ISA, 4.6.4);
- MMU option (ISA, 4.6.5).

Cache control attribute bits are not used by this implementation.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
