Enable QtSerialPort on QNX

On QNX, the combination (IHFLOW | OHFLOW) is equivalent to the CRTSCTS flag.
Only /dev/ser* ports can be enumerated.

Tested on SVTronics UEVM5432 Omap5 board with QNX 6.6

Change-Id: I64b149258a525835e63f231b5291fa86637e3d2a
Reviewed-by: Laszlo Papp <lpapp@kde.org>