[`FA`] Generalize fa config checks and fix flags (#43121)
* fix fa checks
* oops
* yea makes sense
* fix
* did not intend to add this
* fixup tests and wrong flags
* fix
* style
* restrict target guided attn
* remove sam and sam hq (dont support fa anyways), make it fallback as per internal discussion
* missed this one
* move check to separate function
* style
* sync changes with main
* force non ambiguity + nit
