drm/amd/pm: add flood detection for wbrf events

To protect PMFW from being overloaded.

Signed-off-by: Evan Quan <quanliangl@hotmail.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>