Documentation: coresight: Add cc_threshold tunable

This updates config option to include 'cc_threshold' tunable value.

Cc: Suzuki K Poulose <[e-mail]>
Cc: Mike Leach <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Reviewed by: Mike Leach <[e-mail]>
Signed-off-by: Anshuman Khandual <[e-mail]>
Signed-off-by: Suzuki K Poulose <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/trace/coresight/coresight.rst

···
    * - timestamp
      - Session local version of the system wide setting: :ref:`ETMv4_MODE_TIMESTAMP
        <coresight-timestamp>`
+   * - cc_threshold
+     - Cycle count threshold value. If nothing is provided here or the provided value is 0, then the
+       default value i.e 0x100 will be used. If provided value is less than minimum cycles threshold
+       value, as indicated via TRCIDR3.CCITMIN, then the minimum value will be used instead.
 
 How to use the STM module
 -------------------------