[SPARC64]: Use SPARSEMEM_STATIC

Decrease the SECTION_SIZE_BITS --> MAX_PHYSADDR_BITS
range a little bit.

The cost of going to SPARSEMEM_STATIC becomes 8K of BSS space, and in
return we save a pointer dereferences on every page struct lookup.
Even better we hit the main kernel image for the base address which is
in a hugepage locked TLB entry.

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