add usb storage for turris omnia

ideally we would make this a module instead of compiling in
directly

modules/usb.nix

@@ -0,0 +1,31 @@
+# support for USB block devices and the common filesystems
+# they're likely to provide
+
+{lib, config, ... }:
+{
+  kernel = {
+    config = {
+      USB = "y";
+      USB_EHCI_HCD = "y";
+      USB_EHCI_HCD_PLATFORM = "y";
+      USB_OHCI_HCD = "y";
+      USB_OHCI_HCD_PLATFORM = "y";
+      USB_SUPPORT = "y";
+      USB_COMMON = "y";
+      USB_STORAGE = "y";
+      USB_STORAGE_DEBUG = "n";
+      USB_UAS = "y";
+      USB_ANNOUNCE_NEW_DEVICES = "y";
+      SCSI = "y";
+      BLK_DEV_SD = "y";
+      USB_PRINTER = "y";
+      MSDOS_PARTITION = "y";
+      EFI_PARTITION = "y";
+      EXT4_FS = "y";
+      EXT4_USE_FOR_EXT2 = "y";
+      FS_ENCRYPTION = "y";
+
+
+    };
+  };
+}