dm: core: Decouple DM from DT

Some of the DM functions depend on OF_CONTROL, which is incorrect.
DM and DT are orthogonal. Add macro guards around such functions to
avoid compiling them in when DM is enabled, while OF_CONTROL is not.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Simon Glass <sjg@chromium.org>