ARM: shmobile: r8a7778: tidyup #sound-dai-cells settings

ARM: shmobile: r8a7778: tidyup #sound-dai-cells settings

Renesas sound driver needs #sound-dai-cells settings, but, this usage
is a little bit confusable. It came from ALSA SoC historical reasons.
The sound DAI naming method is different between Single/Multi DAI in
the ALSA framework, and it is used for sound card matching.
And this #sound-dai-cells has relationship to it.
Current SoC dtsi has #sound-dai-cells = <1> as default settings
(= it is assuming that board/platform has multi DAI), and
board/platform side needs to overwrite it if board/platform was single
DAI. This style is more confusable for users.
This patch removes SoC side default settings, and force to set it by
board/platform side.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>