ASoC: jz4740: Drop lb60 board code

The board now uses the simple-audio-card driver.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Tested-by: Artur Rojek <contact@artur-rojek.eu>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Paul Burton <paul.burton@mips.com>