kernel-install: consider both grub2 and grub2-efi configs

Since EFI boot now also use grub2, update its config too when present.

Reported-by: @JarrahG
QubesOS/qubes-issues#4902

system-config/kernel-grub2.install

@@ -19,5 +19,10 @@ case "$COMMAND" in
         ;;
 esac
 if [ -x /usr/sbin/grub2-mkconfig ]; then
-    grub2-mkconfig -o /boot/grub2/grub.cfg
+    if [ -e /boot/grub2/grub.cfg ]; then
+        grub2-mkconfig -o /boot/grub2/grub.cfg
+    fi
+    if [ -e /boot/efi/EFI/qubes/grub.cfg ]; then
+        grub2-mkconfig -o /boot/efi/EFI/qubes/grub.cfg
+    fi
 fi