samsung: Drop board_enable_audio_codec()

This function is not needed now since the audio codecs have been converted
to proper drivers. The codec-enable GPIO is handled there.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Minkyu Kang <mk7.kang@samsung.com>