moby: add support for building EFI bootable Moby images

Wrap a EFI stub loader with vmlinuz, initrd, and a short commandline
inside a single EFI binary.

Two files are generated:
- mobylinux.efi is a raw EFI file which some hypervisors can boot directly
- mobylinux-efi.iso: ISO image with just MobyLinux in the EFI partition

also:
- rename legacy BIOS mobylinux.iso to mobylinux-bios.iso
- Build mobylinux-efi.iso as part of the standard mobylinux build

Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>

alpine/docker-compose.yml

@@ -5,16 +5,24 @@ services:
       context: .
     network_mode: bridge
     volumes:
-     - .:/mnt
+      - .:/mnt
+  efi:
+    privileged: true
+    build:
+      context: .
+      dockerfile: Dockerfile.efi
+    network_mode: bridge
+    volumes:
+      - .:/mnt
+  bios:
+    build:
+      context: .
+      dockerfile: Dockerfile.bios
+    network_mode: bridge
+    volumes:
+      - .:/mnt
   arm:
     build:
       context: .
       dockerfile: Dockerfile.armhf
     network_mode: bridge
-  iso:
-    build:
-      context: .
-      dockerfile: Dockerfile.iso
-    network_mode: bridge
-    volumes:
-     - .:/mnt