Change posttrans script to install grub-efi configuration

Remove xen.cfg modification code.
Clone grub-legacy configuration update code and modify to update EFI configuration
Remove comment stating that grub does not support xen in efi mode.

kernel.spec.in

@@ -514,19 +514,18 @@ if [ -f /etc/default/grub ]; then
     fi
 fi
 
-if [ -f /boot/efi/EFI/qubes/xen.cfg ]; then
-    if ! grep -q plymouth.ignore-serial-consoles /boot/efi/EFI/qubes/xen.cfg; then
-        sed -i 's/kernel=.*/& plymouth.ignore-serial-consoles/g' /boot/efi/EFI/qubes/xen.cfg
-    fi
-fi
-
 /bin/kernel-install add %{kernelrelease} /boot/vmlinuz-%{kernelrelease} || exit $?
 
-# grubby (used by new-kernel-pkg) do not understand xen entries in grub2 config
+# Generate legacy boot grub config
 if [ -x /sbin/new-kernel-pkg -a -e /boot/grub2/grub.cfg ]; then
     grub2-mkconfig > /boot/grub2/grub.cfg
 fi
 
+# Generate EFI boot grub config
+if [ -x /sbin/new-kernel-pkg -a -e /boot/efi/EFI/qubes/grub.cfg ]; then
+    grub2-mkconfig > /boot/efi/EFI/qubes/grub.cfg
+fi
+
 %preun
 /bin/kernel-install remove %{kernelrelease} /boot/vmlinuz-%{kernelrelease} || exit $?