[TF-M] [Core Patch] Core: switch signal wait object to 'condition'

Hi, I will update the wait object from 'event' to 'condition'. This is mainly for fixing the issue: https://developer.trustedfirmware.org/T273

'event' is actually a depth 1 semaphore, which is not good enough for signals synching case. Involve a simpler sync object 'condition' for signals (and client ACKs): https://review.trustedfirmware.org/c/trusted-firmware-m/+/712

Please help to check if you are interested in it.

Thanks

-Ken