fix Pi build: force initrd modules to exclude x86 hardware

sd-image.nix imports all-hardware.nix which adds modules like dw-hdmi
that don't exist in the RPi4 kernel. mkForce the availableKernelModules
list to only include Pi-relevant modules.

hosts/cryodev-pi/sd-image.nix

@@ -27,4 +27,12 @@
     "vfat"
     "ext4"
   ];
+
+  # sd-image.nix imports all-hardware.nix which adds x86 modules like dw-hdmi
+  # that don't exist in the RPi4 kernel. Filter them out.
+  boot.initrd.availableKernelModules = lib.mkForce [
+    "xhci_pci"
+    "usbhid"
+    "usb_storage"
+  ];
 }