drm/amdkfd: Add perf counters to topology

For hardware blocks whose performance counters are accessed via MMIO
registers, KFD provides the support for those privileged blocks.

IOMMU is one of those privileged blocks. Most performance counter properties
required by Thunk are available at /sys/bus/event_source/devices/amd_iommu.

This patch adds properties to topology in KFD sysfs for information not
available in /sys/bus/event_source/devices/amd_iommu. They are shown at
/sys/devices/virtual/kfd/kfd/topology/nodes/0/perf/iommu/ formatted as
/sys/devices/virtual/kfd/kfd/topology/nodes/0/perf/<block>/<property>, i.e.
/sys/devices/virtual/kfd/kfd/topology/nodes/0/perf/iommu/max_concurrent.

For dGPUs, who don't have IOMMU, nothing appears under
/sys/devices/virtual/kfd/kfd/topology/nodes/0/perf.

Signed-off-by: Amber Lin <Amber.Lin@amd.com>
Signed-off-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>