sound: Add uclass operations for beeping

Some audio codecs such as Intel HDA do not need to use digital data to
play sounds, but instead have a way to emit beeps. Add this interface as
an option. If the beep interface is not supported, then the sound uclass
falls back to the I2S interface.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>