gnu: grub: Add locale output for bootloading.

* gnu/packages/bootloaders.scm (grub): Add needed modules and new output
generated with new phase 'install-locale-folder.
---
 gnu/packages/bootloaders.scm | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)