Create a function util and cache the results for `has_deepgemm`, `has_deepep`, `has_pplx`

[yewentao256]

nit: create a function and cache the results.

Originally posted by @houseroad in #20090 (comment)

Thanks to @houseroad, there are a lot of code like

has_pplx = importlib.util.find_spec("pplx_kernels") is not None anywhere.

Same for has_deepgemm, has_deepep etc.

We can create util function and cache the result for better readability and maintainablility.

I will have a pr for this soon.