User can check and set the enablement of throttling logging and
the interval between each logging.

V2: simplify the sysfs interface(no string parsing)
V3: add proper lock protection on updating throttling_logging_rs.interval
V4: documentation cosmetic per Luben's suggestion
Signed-off-by: NEvan Quan <evan.quan@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NLuben Tuikov <luben.tuikov@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>