SUMMA GEMM with A stationnary

This MR integrates the work from @AntJego and @rperesso. Please, you should both review this request, such that we can move forward with the SYMM integration. @fpruvost and @agullo Don't hesitate to give feedbacks.

cmake_modules/local_subs.py

@@ -41,6 +41,7 @@ _extra_blas = [
     ('',                     'sgepdf',               'dgepdf',               'cgepdf',               'zgepdf'              ),
     ('',                     'scesca',               'dcesca',               'ccesca',               'zcesca'              ),
     ('',                     'sgesum',               'dgesum',               'cgesum',               'zgesum'              ),
+    ('',                     'sgersum',              'dgersum',              'cgersum',              'zgersum'             ),
 ]
 
 _extra_BLAS = [ [ x.upper() for x in row ] for row in _extra_blas ]