unix: dboot should use efi memory map if present
Current dboot is using multiboot_tag_mmap tag to build memory maps, but this tag is used to store SMAP data. UEFI systems do provide us multiboot_tag_efi_mmap and we should use it. Our boot loader does provide us both tags, but really should fix this.
Testing done: compare dboot memlist with one we get from smap command in loader.