[SPARC64]: Add of_device layer and make ebus/isa use it.

Sparcspkr and power drivers are converted, to make sure it works.
Eventually the SBUS device layer will use this as a sub-class.

I really cannot cut loose on that bit until sparc32 is given the
same infrastructure.

Signed-off-by: David S. Miller <davem@davemloft.net>