[installer] Create a blank grubenv if doesn't exist. (#17216)

- 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
1. Install image from ONiE
2. Run BIOS firmware upgrade

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

installer/default_platform.conf

@@ -264,6 +264,14 @@ 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.
@@ -346,6 +354,14 @@ 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 {} \;)