convert existing raw comments into kernel-doc format as well
as add new documentation

v2: reword the overview
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NNayan Deshmukh <nayan26deshmukh@gmail.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Acked-by: NDaniel Vetter <daniel@ffwll.ch>