hns3 udma: cmd and mailbox for hns3-udma driver

driver inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I85R2F


CVE: NA

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This patch add feature of cmd and mailbox for
hns3-udma driver.

There are two mode of cmd: polling mode and event
mode.

Signed-off-by: Weibo Zhao <zhaoweibo3@huawei.com>