Update Features2 to display SDBG capability of processor. This is
showing up on Haswell-class CPUs

From the Intel SDM, "Table 3-20. Feature Information Returned in the
ECX Register"

11 | SDBG | A value of 1 indicates the processor supports
IA32_DEBUG_INTERFACE MSR for silicon debug.

Submitted by: jiashiun@gmail.com
Reviewed by: jhb neel
MFC after: 2 weeks