Driver core: move dev_get/set_drvdata to drivers/base/dd.c

No one should directly access the driver_data field, so remove the field
and make it private.  We dynamically create the private field now if it
is needed, to handle drivers that call get/set before they are
registered with the driver core.

Also update the copyright notices on these files while we are there.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>