i2c: add phytium i2c driver DT binding docs

phytium inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8AXAT


CVE: NA

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Add Phytium i2c driver DT bindings documents.

Signed-off-by: Jiakun Shuai <shuaijiakun1288@phytium.com.cn>
Signed-off-by: Chen Baozi <chenbaozi@phytium.com.cn>