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>

Author: Junhao He

Documentation/admin-guide/perf/hisi-pmu.rst

@@ -98,6 +98,14 @@ CCL/ICL-ID. For I/O die, the ICL-ID is followed by:
 5'b00011: HAC_ICL;
 5'b10000: PCIe_ICL;
 
+(e) uring_channel: UC PMU events 0x47~0x59 supports filtering by tx request
+uring channel. It is 2 bits. Some important codes are as follows:
+2'b11: count the events which sent to the uring_ext (MATA) channel;
+2'b01: is the same as 2'b11;
+2'b10: count the events which sent to the uring (non-MATA) channel;
+2'b00: default value, count the events which sent to the both uring and
+       uring_ext channel;
+
 Users could configure IDs to count data come from specific CCL/ICL, by setting
 srcid_cmd & srcid_msk, and data desitined for specific CCL/ICL by setting
 tgtid_cmd & tgtid_msk. A set bit in srcid_msk/tgtid_msk means the PMU will not