[IA64] re-enable preempt before page allocation for pgtable quicklist

This is a fix to the pgtable_quicklist code.  There is a GFP_KERNEL
allocation in pgtable_quicklist_alloc(), which spews the usual warnings
if the kernel is under heavy VM pressure and the reclaim code is
invoked.  re-enable preempt before we allocate the new page.

This patch is against 2.6.12-rc2-mm2

Signed-off-by: Martin Hicks <mort@sgi.com>
Signed-off-by:  Tony Luck <tony.luckintel.com>