sparc64: Rewrite central driver.

This driver is now limited to just doing the basic clock board and FHC
chip initialization and registering the platform devices for the
per-board LEDs, which are driven by the new LEDS_STARFIRE driver.

The IRQ register handling is already confined purely to the device
tree code.

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