Adjustments to the automake-based build

- Enabled the appropriate macros so that alsa and pulseaudio drivers
  are enabled in src/sound.c.
- Replace DRIVER_QNX and DRIVER_ALSA05 for SOUND_QNX and SOUND_ALSA05
- Change SOUND_PULSE to SOUND_PULSEAUDIO to keep naming consistent

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>