ASoC: rockchip: i2s: Fix Kconfig for I2S device driver

Currently, CONFIG_SND_SOC_ROCKCHIP_I2S could also be selected
without having CONFIG_SND_SOC_ROCKCHIP enabled.

As this makes no sense, a Kconfig dependency is added to
CONFIG_SND_SOC_ROCKCHIP_I2S. This will make the item visible only if
CONFIG_SND_SOC_ROCKCHIP is enabled.

Additionally, as the code connected to CONFIG_SND_SOC_ROCKCHIP_I2S
depends on CONFIG_SND_SOC_GENERIC_DMAENGINE_PCM, the dependency
is moved to reflect this more clearly.

Signed-off-by: Andreas Ruprecht <rupran@einserver.de>
Reported-by: Jim Davis <jim.epost@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>