sparc: unify openprom.h

After the preparational steps the unification was simple.

The linux_prom_pci_registers definition did not look like
it could be unified at first look since the structure is assigned
using prop_getproperty() / of_get_property() so the structure
is assumed to come direct form the prom.

The LINUX_OPPROM_MAGIC was kept even if it is not used by the kernel
on the assumption that userspace may require it.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>