Get UEFI command line via `EFI_LOADED_IMAGE_PROTOCOL`

Currently, we read from a `hermit-bootargs` file.

It would be useful to get the image's load options via the [`EFI_LOADED_IMAGE_PROTOCOL`](https://uefi.org/specs/UEFI/2.11/09_Protocols_EFI_Loaded_Image.html) ([`LoadedImage`](https://docs.rs/uefi/0.36.1/uefi/proto/loaded_image/struct.LoadedImage.html)) instead.