of/sparc: convert various prom_* functions to use phandle

Rather than passing around ints everywhere, use the
phandle type where appropriate for the various functions
that talk to the PROM.

Signed-off-by: Andres Salomon <dilinger@queued.net>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>