The initramfs needs ext4 (to mount the rootfs) and usb_f_rndis
(to enable USB networking on devices that use USB configfs).
If these are built as modules, they need to be included in initramfs.
[ci:skip-build]: already built successfully in CI
This device is x86_64 and has a 32-bit UEFI, so I need to install
32-bit grub (AFAIK it's the only bootloader capable of loading a 64-bit
kernel from 32-bit).
The grub-efi-x86 package has been generated with pmbootstrap.