dm: core: Add a function to find a device by drvdata

It is sometimes useful to find a device in a uclass using only its driver
data. The driver data often indicates the 'subtype' of the device, e,g,
via its compatible string.

Add a function to handle this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>