[IA64-SGI] move nodepda pointer out of pda

Remove the p_nodepda and p_subnodepda pointers from the pda_s structure.
And then define a new per-cpu pointer to the nodepda and export it so
that it can be accessed by kernel modules.

Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>