Improve cputemp(4) driver wrt newer Intel processors, especially

Improve cputemp(4) driver wrt newer Intel processors, especially
Xeon 5500/5600 series:

 - Utilize IA32_TEMPERATURE_TARGET, a.k.a. Tj(target) in place
   of Tj(max) when a sane value is available, as documented
   in Intel whitepaper "CPU Monitoring With DTS/PECI"; (By sane
   value we mean 70C - 100C for now);
 - Print the probe results when booting verbose;
 - Replace cpu_mask with cpu_stepping;
 - Use CPUID_* macros instead of rolling our own.

Approved by:	rpaulo
MFC after:	1 month