drm/amdgpu: added a sysfs interface for thermal throttling related V4

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: Evan Quan <evan.quan@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>