xen: separate p2m allocation from setting

When doing very early p2m setting, we need to separate setting
from allocation, so split things up accordingly.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

arch/x86/xen/mmu.h

@@ -11,6 +11,9 @@ enum pt_level {
 };
 
 
+bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn);
+bool install_p2mtop_page(unsigned long pfn, unsigned long *p);
+
 void set_pte_mfn(unsigned long vaddr, unsigned long pfn, pgprot_t flags);