Simplify rwlock implementation.

Simplify rwlock implementation.

Remove RW_COUNT() from the rwlock implementation.  The idea was that it
could be used as a generic wrapper for getting at the internal state
of a rwlock.  While a good idea it's proven problematic to keep it
correct for multiple archs and internal implementation changes.  In
short it hasn't been worth the trouble.

With that and simplicity in mind things have been updated to use the
rwsem_is_locked() function instead of RW_COUNT for the RW_*_HELD()
functions.  As for rw_upgrade() it remains only implemented for
the generic rwsem implemenation.  It remains to be determined if its
worth the effort of adding a custom implementation for each arch.