qspi: add phytium qspi driver DT binding docs

phytium inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8CAKU


CVE: NA

---------------------------------------------------------

Add Phytium qspi driver DT bindings documents.

Signed-off-by: Malloy Liu <liuqi1610@phytium.com.cn>