[boot] Build, load, and pass initrd from boot to init

The initrd image is now created by the build system, loaded by the
bootloader, and passed to srv.init, which loads it (but doesn't do
anything with it yet, so this is actually a functional regression).

This simplifies a lot of the modules code between boot and init as well:
Gone are the many subclasses of module and all the data being inline
with the module structs, except for any loaded files. Now the only
modules loaded and passed will be the initrd, and any devices only the
bootloader has knowledge of, like the UEFI framebuffer.

assets/manifests/test.yaml

@@ -1,9 +1,13 @@
 ---
+location: jsix
 init: srv.init
+initrd:
+  name: initrd.dat
+  format: zstd
 flags: ["test"]
-programs:
-  - name: panic.serial
-    target: kernel
-    flags: panic
-  - name: drv.uart
-  - name: test_runner
+panic:
+  - panic.serial
+services:
+  - test_runner
+drivers:
+  - drv.uart