image: Use grub-efi to install the EFI bootloader.

* gnu/build/image.scm (initialize-efi-partition): Rename bootloader-package
argument to grub-efi.
* gnu/system/image.scm (system-disk-image): Adapt accordingly to pass
grub-efi package.

gnu/build/image.scm

@@ -146,10 +146,10 @@ deduplicates files common to CLOSURE and the rest of PREFIX."
 
 (define* (initialize-efi-partition root
                                    #:key
-                                   bootloader-package
+                                   grub-efi
                                    #:allow-other-keys)
   "Install in ROOT directory, an EFI loader using BOOTLOADER-PACKAGE."
-  (install-efi-loader bootloader-package root))
+  (install-efi-loader grub-efi root))
 
 (define* (initialize-root-partition root
                                     #:key

gnu/system/image.scm

@@ -234,6 +234,7 @@ used in the image."
                               #:references-graphs '#$graph
                               #:deduplicate? #f
                               #:system-directory #$os
+                              #:grub-efi #+grub-efi
                               #:bootloader-package
                               #+(bootloader-package bootloader)
                               #:bootloader-installer