dm: core: Allocate platform data when binding a device

When using allocated platform data, allocate it when we bind the device.
This makes it possible to fill in this information before the device is
probed.

This fits with the platform data model (when not using device tree),
since platform data exists at bind-time.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Masahiro Yamada <yamada.m@jp.panasonic.com>