core: extend struct driver_info to point to device

Currently when creating an U_BOOT_DEVICE entry a struct driver_info
is declared, which contains the data needed to instantiate the device.
However, the actual device is created at runtime and there is no proper
way to get the device based on its struct driver_info.

This patch extends struct driver_info adding a pointer to udevice which
is populated during the bind process, allowing to generate a set of
functions to get the device based on its struct driver_info.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>
Reviewed-by: Simon Glass <sjg@chromium.org>