docs: perf: Add new description for HiSilicon UC PMU

A new function is added on HiSilicon uncore UC PMU.

The UC PMU support to filter statistical information based on
the specified tx request uring channel. Make user configuration
through "uring_channel" parameter.
Document them to provide guidance on how to use them.

Signed-off-by: Junhao He <hejunhao3@huawei.com>
Reviewed-by: Jonathan Cameron <Jonthan.Cameron@huawei.com>
Reviewed-by: Yicong Yang <yangyicong@hisilicon.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20230615125926.29832-4-hejunhao3@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>