i2c: mvtwsi: Add support for DM clocks and resets

The controller may need to have clocks/resets enabled for it to work.
Add support for this. Since the clocks/resets are optional on some
platforms (per the device tree binding), do not prevent probing the
controller if they are missing.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Heiko Schocher <hs@denx.de>