polyunfill: don't ship x86-only kernel modules to moby's initrd

notably, this relaxes some constraints on the kernel so that e.g.
postmarketOS kernel actually passes eval checks (and boots to ssh!
no graphics yet)

hosts/common/hardware/x86_64.nix

@@ -7,6 +7,17 @@
       "usb_storage"   # rpi needed this to boot from usb storage, i think.
       "nvme"  # to boot from nvme devices
       # efi_pstore evivars
+
+      # added (speculatively) 2024/05/21; these were implicitly being added by nixos/modules/system/boot/kernel.nix
+      # i've copied not all of them, but most
+      "mmc_block"
+      "dm_mod"
+      # USB keyboards
+      "uhci_hcd" "ehci_hcd" "ehci_pci" "ohci_hcd" "ohci_pci" "xhci_hcd" "xhci_pci" "usbhid" "hid_generic" "hid_lenovo" "hid_apple" "hid_roccat" "hid_logitech_hidpp" "hid_logitech_dj" "hid_microsoft" "hid_cherry" "hid_corsair"
+      # x86 keyboard stuff
+      "pcips2" "atkbd" "i8042"
+      # stage-2 init needs rtc?
+      "rtc_cmos"
     ];
 
     hardware.cpu.amd.updateMicrocode = true;    # desktop

hosts/common/polyunfill.nix

@@ -73,4 +73,16 @@
   # see: <nixos/modules/tasks/swraid.nix>
   # it was enabled by default before 23.11
   boot.swraid.enable = lib.mkDefault false;
+
+  # see: <nixos/modules/system/boot/kernel.nix>
+  # by default, it adds to boot.initrd.availableKernelModules:
+  # - SATA: "ahci" "sata_nv" "sata_via" "sata_sis" "sata_uli" "ata_piix" "pata_marvell"
+  # - "nvme"
+  # - scsi: "sd_mod" "sr_mod"
+  # - SD/eMMC: "mmc_block"
+  # - USB keyboards: "uhci_hcd" "ehci_hcd" "ehci_pci" "ohci_hcd" "ohci_pci" "xhci_hcd" "xhci_pci" "usbhid" "hid_generic" "hid_lenovo" "hid_apple" "hid_roccat" "hid_logitech_hidpp" "hid_logitech_dj" "hid_microsoft" "hid_cherry" "hid_corsair"
+  # - LVM: "dm_mod"
+  # - on x86 only: more keyboard stuff: "pcips2" "atkbd" "i8042"
+
+  boot.initrd.includeDefaultModules = lib.mkDefault false;
 }