Add bit definitions for Intel PT MSRs to support trace output
directed to the memeory subsystem and holds a count if packet
bytes that have been sent out.

These are required by the upcoming PT support in KVM guests
for MSRs read/write emulation.
Signed-off-by: Luwei Kang <luwei.kang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>