Sound: Add command for audio playback

This patch adds command to test audio playback.
sound init - Initialises the audio subsystem (i2s and wm8994 codec)
sound play - Plays predefined the audio data when specified length
and frequency.

Signed-off-by: Rajeshwari Shinde <rajeshwari.s@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>