fbdev: sh_mobile_hdmi: Add select SND_SOC to Kconfig

This patch solve compile error when .config doesn't have
CONFIG_SND_SOC which is needed for HDMI sound.
It was reported by Guennadi as follows

Besides, I think, this will not link without CONFIG_SND_SOC.
Reported-by: NGuennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: NKuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: NGuennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: NLiam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

drivers/video/Kconfig

@@ -1919,6 +1919,7 @@ config FB_SH_MOBILE_HDMI
 	tristate "SuperH Mobile HDMI controller support"
 	depends on FB_SH_MOBILE_LCDC
 	select FB_MODE_HELPERS
+	select SND_SOC
 	---help---
 	  Driver for the on-chip SH-Mobile HDMI controller.