Return EOPNOTSUPP instead of EINVAL if a PMC allocation request specifies a PMC capability (e.g., sampling) that is not supported by hardware.  Return EINVAL early if the PMC class passed in is not recognized.
Return EOPNOTSUPP instead of EINVAL if a PMC allocation request
specifies a PMC capability (e.g., sampling) that is not supported
by hardware.  Return EINVAL early if the PMC class passed in is
not recognized.

MFC after:	3 days

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