ANDROID: ASoC: add hikey960-i2s DT bindings

Adds DT bindings documentation for
the hikey960-i2s driver and audio card device.

Bug: 146450171
Signed-off-by: Youlin Wang <wangyoulin1@hisilicon.com>
Signed-off-by: Tanglei Han <hantanglei@huawei.com>
Signed-off-by: Guangke Ji <jiguangke@huawei.com>
Signed-off-by: Feng Chen <puck.chen@hisilicon.com>
Signed-off-by: Kaihua Zhong <zhongkaihua@huawei.com>
Signed-off-by: Jun Chen <chenjun14@huawei.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Yiping Xu <xuyiping@hisilicon.com>
Signed-off-by: Pengcheng Li <lipengcheng8@huawei.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Change-Id: If9f8ce65c78e1e1e6b2e0439b590e7558763d631