sparc: Use sparc64 version of prom/printf.c

Use sparc64 version of prom/printf.c.

The only differences for sparc32 is that prom_printf is no longer
exported for modules which should be OK.

Signed-off-by: Robert Reif <reif@earthlink.net>
Signed-off-by: David S. Miller <davem@davemloft.net>