Figure out every function's work

[scw00]

• [ ] vm_phys_add_seg
• [ ] vm_phys_alloc_contig
• [ ] vm_phys_alloc_freelist_pages
• [x] vm_phys_alloc_pages
• [ ] vm_phys_domain_intersects
• [ ] vm_phys_fictitious_reg_range
• [ ] vm_phys_fictitious_unreg_range
• [ ] vm_phys_fictitious_to_vm_page
• [ ] vm_phys_free_contig
• [ ] vm_phys_free_pages
• [ ] vm_phys_init
• [ ] vm_phys_paddr_to_vm_page
• [ ] vm_phys_scan_contig
• [ ] vm_phys_set_pool
• [ ] vm_phys_unfree_page
• [ ] vm_phys_zero_pages_idle
• [ ] vm_phys_mem_affinity

[scw00]

vm_phys_alloc_pages allocate contiguous pages from one flind(DMA or LOWEr etc) and one domain it should not cross domain and flind.