cpu: de-duplicate some of the operators and refactor

[cmdr2]

Note: This PR only deletes lines from ggml-cpu.c, it does not modify any functions in it. I'm not sure why git diff tries to combine them as changes. Standard diff shows the correct diff of ggml-cpu.c: https://gist.github.com/cmdr2/a76df5af311417619788e8330b1908b3

This PR de-duplicates some of the easily-templatized functions in ggml-cpu.c. It takes inspiration from binbcast.cu and common.cuh.

• Binary: add, sub, mul, div
• Unary: abs, sgn, neg, step, tanh, elu, relu, sigmoid, hardsigmoid, exp, hardswish, sqr, sqrt, sin, cos, log

This removes the op implementation functions from ggml-cpu.c (around 2000 lines). As a side-effect, all the functions now support bf16 as well as non-contiguous src1.

The performance is the same as the current implementation. It also passes all the runners on ggml-ci, which tested non-contiguous inputs (in SAM) and vDSP on Mac.