cxl: Calculate region bandwidth of targets with shared upstream link

The current bandwidth calculation aggregates all the targets. This simple
method does not take into account where multiple targets sharing under
a switch or a root port where the aggregated bandwidth can be greater than
the upstream link of the switch.

To accurately account for the shared upstream uplink cases, a new update
function is introduced by walking from the leaves to the root of the
hierarchy and clamp the bandwidth in the process as needed. This process
is done when all the targets for a region are present but before the
final values are send to the HMAT handling code cached access_coordinate
targets.

The original perf calculation path was kept to calculate the latency
performance data that does not require the shared link consideration.
The shared upstream link calculation is done as a second pass when all
the endpoints have arrived.

Testing is done via qemu with CXL hierarchy. run_qemu[1] is modified to
support several CXL hierarchy layouts. The following layouts are tested:

HB: Host Bridge
RP: Root Port
SW: Switch
EP: End Point

2 HB 2 RP 2 EP: resulting bandwidth: 624
1 HB 2 RP 2 EP: resulting bandwidth: 624
2 HB 2 RP 2 SW 4 EP: resulting bandwidth: 624

Current testing, perf number from SRAT/HMAT is hacked into the kernel
code. However with new QEMU support of Generic Target Port that's
incoming, the perf data injection is no longer needed.

[1]: https://github.com/pmem/run_qemu

Suggested-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://lore.kernel.org/linux-cxl/20240501152503.00002e60@Huawei.com/
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Link: https://patch.msgid.link/20240904001316.1688225-3-dave.jiang@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

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