arm64: dts: add Hi6220 spi configuration nodes

Add Hi6220 spi configuration nodes. Disable by default in hi6220.dtsi
and enable it in board dts for usage of 96boards LS mezzanine board.

Signed-off-by: Zhong Kaihua <zhongkaihua@huawei.com>
Signed-off-by: Guodong Xu <guodong.xu@linaro.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>