Refactor of the QSerialPortInfo for OS X

The current implementation of the qserialportinfo_mac.cpp module is a
little confused and complicated.

It is reasonable to re-write it using some ready wrappers of CFTypeRef,
CFStringRef and others objects from the private qcore_mac_p.h file.

Thus, it will allow to bypass of manual releasing of the allocated
resources (using the RAII idiom where it is possible), and also to
simplify a code.

Tested on OS X 10.8.4 with the on-board, USB PL2303, USB FTDI,
USB Android serial ports and with the USB ZTE Modem using Qt4.

Change-Id: Ibbac03a17fdd41bbaf530f863e7c690a15708bd2
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Denis Shienkov <denis.shienkov@gmail.com>