[SPARC64]: Privatize sun4u_get_pte() and fix name.

__get_phys is only called from init.c as is prom_virt_to_phys(),
__get_iospace() is not called at all, and sun4u_get_pte() is largely
misnamed.

Privatize the implementation and helper functions of
sun4u_get_phys() to mm/init.c, and rename to
kvaddr_to_paddr().

The only used of this thing is flush_icache_range(), and thus
things can be considerably further simplified.  For example,
we should only see module or PAGE_OFFSET kernel addresses here,
so we don't need the OBP firmware range handling at all.

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