[IA64] ioremap() should prefer WB over UC

efi_memmap_init() collects full granules of WB memory, without
regard for whether they also support UC.  So in order for ioremap()
to work for main memory, it must prefer WB mappings when possible.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>