efi_loader: make efi_disk_create_partitions a global symbol

Up to now we have been using efi_disk_create_partitions() to create
partitions for block devices that existed before starting an EFI
application.

We need to call it for block devices created by EFI
applications at run time. The EFI application will define the
handle for the block device and install a device path protocol
on it. We have to use this device path as stem for the partition
device paths.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>