greybus: camera: Reset link speed on failed config

Improve the management of unipro power mode changes in response
to a configure_stream operation.
When sending a "test only" request to camera module, do not change power
mode to HS-G2 as no frame will be actually transmitted.
When receiveing an "adjusted" configuration response, reset power
mode to PWM-G1.

Signed-off-by: Jacopo Mondi <jacopo.mondi@linaro.org>
Reviewed-by: Gjorgji Rosikopulos <grosikopulos@mm-sol.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>