Rename AE_FMT_S24xE4 to AE_FMT_S24xE4H to indicate upper 3 bytes are used
Make S24xE4H conversions always act on upper 3 bytes
Introduce new formats AE_FMT_S24xE4L which use the lower 3 bytes of a 4 byte word
Use AE_FMT_S24xE4L in conjunction with ALSA and PulseAudio
Remove unneccessary mask operations in Float_S24NE4H
Avoid intermediate floating point conversion when outputting S24NE4L