[SPARC] openprom: implement ->compat_ioctl

implement a compat_ioctl handle in the driver instead of having table
entries in sparc64 ioctl32.c (I plan to get rid of the arch ioctl32.c
file eventually)

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>