Domain buddy allocator

include/mem/domain.h

• void domain_buddies_init(void)
• void domain_free(paddr_t address,size_t page_count)
• paddr_tdomain_alloc(size_t pages,enum alloc_flags flags)
• paddr_tdomain_alloc_from_domain(struct domain *cd,size_t pages)
• void domain_buddy_dump(void)
• void domain_buddies_init_late()
• struct domain *domain_for_addr(paddr_t addr)