INTEL_FAM6_ATOM_SILVERMONT_MID/INTEL_FAM6_ATOM_AIRMONT_MID are not
listed in probe_nhm_msrs(). This means that most of the turbostat
features are not available on these two platforms.

Further more, checking for these two models in has_slv_msrs() is
dead code. Because has_slv_msrs() is called by the code guarded by
probe_nhm_msrs().

For these two reasons, remove pseudo check for
INTEL_FAM6_ATOM_SILVERMONT_MID and INTEL_FAM6_ATOM_AIRMONT_MID.

Will add back the support when we can access these two platforms.
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>