dm: Introduce DMA constraints into the core device model

Calculating the DMA offset between a bus address space and CPU's every
time we call phys_to_bus() and bus_to_phys() isn't ideal performance
wise, as it implies traversing the device tree from the device's node up
to the root. Since this information is static and available before the
device's initialization, parse it before the probe call an provide the
DMA offset in 'struct udevice' for the address translation code to use
it.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Matthias Brugger <mbrugger@suse.com>