util/grub.d/00_header.in: Disable loading all_video for EFI

Loading all_video for EFI can cause video issues in some cases
since GRUB Bochs/Cirrus drivers may conflict with native EFI drivers.
Change default behavior for EFI to only load EFI specific video
modules. Also include a new environment variable to restore the old
behavior if needed.

Fixes: https://savannah.gnu.org/bugs/?66200

Signed-off-by: Andrew Hamilton <adhamilt@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

util/grub-mkconfig.in

@@ -255,7 +255,8 @@ export GRUB_DEFAULT \
   GRUB_ENABLE_CRYPTODISK \
   GRUB_BADRAM \
   GRUB_OS_PROBER_SKIP_LIST \
-  GRUB_DISABLE_SUBMENU
+  GRUB_DISABLE_SUBMENU \
+  GRUB_FORCE_EFI_ALL_VIDEO
 
 if test "x${grub_cfg}" != "x"; then
   rm -f "${grub_cfg}.new"