Allows to separate the dispatch query cost from the execution of multiple calls to dc_smm_dnn where M, N, and K does not change (homogeneous stack in the notion of CP2K). Documented the functions in xsmm_knc.h. The latter file is now assembled from xsmm_knc.begin, the series of generated prototype declarations (xsmm_knc_geninc.py) and xsmm_knc.end. Code cleanup.