multimedia: add EINTR-safe qt_safe_ioctl helper

ioctl() can fail with EINTR if a signal handler is installed.
Add QtMultimediaPrivate::qt_safe_ioctl to qmultimediautils that
retries on EINTR, and use it at all ioctl call sites instead of
hand-rolled or missing retry loops.

Pick-to: 6.12
Change-Id: I0add9271c662d153f6289ae59cb428d0c64c4f03
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>