RISC-V Atomic Cleanups

RISC-V Atomic Cleanups

This patch set is the result of some feedback that filtered through
after our original patch set was reviewed, some of which was the result
of me missing some email.  It contains:

* A new READ_ONCE in arch_spin_is_locked()
* __test_and_op_bit_ord() is now actually ordered
* Improvements to various comments
* Removal of some dead code