ggml : fix some mul mat cases + add tests for src1 F16 (ggml/669)

* fixed mul-mat error for old GPUs

* style fixes

* add mul mat src1 f16 test cases, fix more cases

ggml-ci

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Co-authored-by: bssrdf <bssrdf@gmail.com>
Co-authored-by: slaren <slarengh@gmail.com>