silmbus: ngd: register controller after power up.

Register slimbus controller only after finishing powerup sequnce so that we
do not endup in situation where core starts sending transactions before
the controller is ready.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>