CONFIG_EFI_MIXED is disabled in SLE and openSUSE.

Even if we official don't support systems with a 32bit EFI firmware, there are
consumer machines out there which have them.
Since we still ship a grub2 capable of booting machines with a pure 32bit EFI
firmware, I did run into a lot of problems since CONFIG_EFI_MIXED was disabled:
- YaST does not detect that this is a EFI system
- efibootmgr cannot access EFI variables
- wlan driver did not work
- reboot does not work

And most likely quite some more.
I don't know which disadvantages this option has, but could we please enable it
at least for openSUSE?