Replace one-shot uses of QSemaphore with QLatch

This commit replaces one-shot synchronization of threads that were using
QSemaphore with QLatch. QSemaphore is efficient on Linux and Windows,
but allocates memory elsewhere. Even on those platforms where we have
futex-like OS support, QSemaphore is heavier than what we really need
here.

There was only one use of QSemaphore in qtsensors.

Change-Id: Ib5ce7a497e034ebabb2cfffd1761a4fcb2be9a6c
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>