With dm-tag feature, any U-Boot subsystem is allowed to associate
arbitrary number of data with a particular udevice. This can been
see as expanding "struct udevice" without modifying the definition.
As a first user, UEFI subsystem makes use of tags to associate
an efi_disk object with a block device.
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
