Revert "efi_loader: remove efi_exit_caches()"

This reverts commit 3170db63.

It reportedly breaks OpenBSD/armv7 booting and I've already received
complaints from people that it breaks some Linux armv7 systems as well.

We'll have to give this whole caching story a good bit more thought.

Reported-by: Jonathan Gray <jsg@jsg.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>