Comments & style cleanup, no functional change intended.

Comments & style cleanup, no functional change intended.

- Sync comments with NetBSD including locking details.
- Remove superfluous parenthesis and spaces.
- Add brackets, even if questionable, to reduce diff with NetBSD
- Use for (;;) instead of while(1)
- Rename a variable from 'result' into 'error'.
- Move uvm_fault() and uvm_fault_upper_lookup()
- Add an locking assert in uvm_fault_upper_lookup()

ok tb@, mlarkin@