ARM: OMAP2+: clockdomain: convert existing atomic usecounts into spinlock-protected shorts/ints

The atomic usecounts seem to be confusing, and are no longer needed
since the operations that they are attached to really should take
place under lock.  Replace the atomic counters with simple integers,
protected by the enclosing powerdomain spinlock.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>