ASoC: ux500: Don't make the CPU I2S driver user selectable

It can only be used with a machine driver so the idiomatic thing for
ASoC is to select this driver from the machine driver.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/ux500/Kconfig

@@ -10,7 +10,5 @@ menuconfig SND_SOC_UX500
 		any of the Ux500 platforms (e.g. U8500).
 
 config SND_SOC_UX500_PLAT_MSP_I2S
-	tristate "Platform - MSP (I2S)"
+	tristate
 	depends on SND_SOC_UX500
-	help
-		Say Y if you want to enable the Ux500 MSP I2S-driver.