tools/power/turbostat: Abstract RAPL divisor support

INTEL_FAM6_ATOM_SILVERMONT model needs a divisor to convert the raw
Energy Units value from MSR_RAPL_POWER_UNIT.

Abstract the support for RAPL divisor.

Delete CPU model check in rapl_probe_intel().

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>