With the advent of the new ACPI hot-plug memory driver and mechanism
is needed to deal with ACPI add memory events that do not contain the
pxm (node) information. I do not believe that the add-event is required
to contain this information so I create a arch_find_node generic layer
used in the generic add_memory function. 

  If add_memory is called with node < 0 arch_find_node is invoked to
fine the correct node to add the memory. This created the generic
construct of arch_find_node. 

   
This was built against 2.6.18-rc2.

Signed-off-by:  Keith Mannthey <kmannth@us.ibm.com>