fwu: check all images for transitioning out of Trial State

The platform transitions out of Trial State into the Regular State
only when all the images in the update bank have been accepted. Check
for this condition before transitioning out of Trial State.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Tested-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>