system: Use locale information in grub.cfg.

* gnu/bootloader/grub.scm (module-declaration): Add (gnu system locale).
(locale-config-entries): New procedure.
(grub-configuration-file): Use locale-config-entries.
---
 gnu/bootloader/grub.scm | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)