[installer] Create a blank grubenv if doesn't exist. (sonic-net#17414)

- Why I did it
To fix BIOS firmware update after fresh image installation from ONiE

- How I did it
Initialized empty GRUB environment file after ONiE installation

- How to verify it
Install image from ONiE
Run BIOS firmware upgrade

Signed-off-by: Nazarii Hnydyn <nazariig@nvidia.com>

installer/default_platform.conf

@@ -264,14 +264,6 @@ demo_install_grub()
         exit 1
     }
 
-    # Create a blank environment block file.
-    if [ ! -f "$onie_initrd_tmp/$demo_mnt/grub/grubenv" ]; then
-        grub-editenv "$onie_initrd_tmp/$demo_mnt/grub/grubenv" create || {
-            echo "ERROR: grub-editenv failed on: $blk_dev"
-            exit 1
-        }
-    fi
-
     if [ "$demo_type" = "DIAG" ] ; then
         # Install GRUB in the partition also.  This allows for
         # chainloading the DIAG image from another OS.
@@ -354,14 +346,6 @@ demo_install_uefi_grub()
     }
     rm -f $grub_install_log
 
-    # Create a blank environment block file.
-    if [ ! -f "$demo_mnt/grub/grubenv" ]; then
-        grub-editenv "$demo_mnt/grub/grubenv" create || {
-            echo "ERROR: grub-editenv failed on: $blk_dev"
-            exit 1
-        }
-    fi
-
     # Configure EFI NVRAM Boot variables.  --create also sets the
     # new boot number as active.
     grub=$(find /boot/efi/EFI/$demo_volume_label/ -name grub*.efi -exec basename {} \;)
@@ -631,6 +615,14 @@ EOF
         umount $demo_mnt
     else
         cp $grub_cfg $onie_initrd_tmp/$demo_mnt/grub/grub.cfg
+
+        # Create a blank environment block file.
+        if [ ! -f "$onie_initrd_tmp/$demo_mnt/grub/grubenv" ]; then
+            grub-editenv "$onie_initrd_tmp/$demo_mnt/grub/grubenv" create || {
+                echo "ERROR: grub-editenv failed on: $blk_dev"
+                exit 1
+            }
+        fi
     fi
 
     cd /