IVGCVSW-3691 Implement SendCounterPacket.SendCounterDirectoryPacket() function

IVGCVSW-3691 Implement SendCounterPacket.SendCounterDirectoryPacket() function

 * Changed the signature of SendCounterDirectoryPacket to accept any
   ICounterDirectory object
 * Added helper methods to the SendCounterPacket class for creating the records
 * Created mock classes for testing
 * Added unit tests for both SendCounterDirectoryPacket and the helper methods
 * Added unit tests for the SWTrace utility functions
 * Added ReadUint8 utility function for getting single byte out of a buffer
 * Disabled extra sign-conversion warning in the conversion macro

Change-Id: Ie2dddcd6824ed07b623f0cd78d9b7d05c5b70c39
Signed-off-by: Matteo Martincigh <matteo.martincigh@arm.com>