initfs: wire driver-manager-initfs into the drivers target

40_drivers.target referenced only pcid-spawner-initfs, so the initfs
driver-manager service (staged, gated, with its storage TOML and the
binary already copied into initfs/bin) never entered the boot graph.
The target now lists driver-manager-initfs first and keeps
pcid-spawner-initfs as the gated fallback — the initfs cutover is
complete. Also correct the initfs-storage.toml header comment (the
content is driver-manager format).

drivers/initfs-storage.toml

@@ -1,4 +1,4 @@
-## Storage drivers for InitFS (pcid-spawner format) ##
+## Storage drivers for InitFS (driver-manager format) ##
 
 [[driver]]
 name = "ahcid"

init.initfs.d/40_drivers.target

@@ -7,6 +7,7 @@ requires_weak = [
     "40_ps2d.service",
     "40_bcm2835-sdhcid.service",
     "40_hwd.service",
+    "40_driver-manager-initfs.service",
     "40_pcid-spawner-initfs.service",
     "41_acpid.service",
 ]