visualiserWin: remove the usage of AVCODEC_MAX_AUDIO_FRAME_SIZE

In later versions of ffmpeg the AVCODEC_MAX_AUDIO_FRAME_SIZE has been
removed and replaced with AVFrame structures that allow ffmpeg to
return a dynamic size of samples according to AVFrame.linesize[plane].

Use a dynamically created buffer rather than a static array.

Signed-off-by: Matthew Leach <matthew.leach@arm.com>
visualiserWin: ensure samples are in the correct format for SDL

SDL expects interleaved S16 audio samples. However, some audio codecs
don't support this format.

Use libswresample to ensure that the samples are in the correct format
before passing off to SDL.
configure.ac: add a check for GLEW

GLEW is now required for allowing easy access to OpenGL
extensions. This will help with shader work.

Signed-off-by: Matthew Leach <matthew.leach@arm.com>
shaders: add the shaders example visualiser

Add a visualiser that is able to load a fragment shader and use FFT
data exported as a uniform to draw to the screen.

Signed-off-by: Matthew Leach <matthew.leach@arm.com>