x86_64: Quicklist support for x86_64

This adds caching of pgds and puds, pmds, pte.  That way we can avoid costly
zeroing and initialization of special mappings in the pgd.

A second quicklist is useful to separate out PGD handling.  We can carry the
initialized pgds over to the next process needing them.

Also clean up the pgd_list handling to use regular list macros.  There is no
need anymore to avoid the lru field.

Move the add/removal of the pgds to the pgdlist into the constructor /
destructor.  That way the implementation is congruent with i386.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: "Luck, Tony" <tony.luck@intel.com>
Acked-by: William Lee Irwin III <wli@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>