Add RDTSCP instruction support for HVM VMX guest.

Add RDTSCP instruction support for HVM VMX guest.

RDTSCP is introduced in Nehalem processor on Intel platform. Like
RDTSC, RDTSCP will return the TSC value, besides, it will return the
low 32bit of TSC_AUX MSR. Currently Linux kernel will write (node_id
<< 12 | process_id) into that MSR, so that when guest execs RDTSCP, it
will also get processor information.  - This instruction is supported
for HVM only when the hardware has this capability (indicated by
cpuid).

Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>