w1: add phytium w1 driver document

phytium inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I85QH1


CVE: NA

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add phytium w1 driver document

Signed-off-by: Wei Tian <tianwei@phytium.com.cn>
Signed-off-by: Chen Baozi <chenbaozi@phytium.com.cn>