This allows use of the powerful ftrace infrastructure.

See Documentation/trace/ for usage information.

[avi, stephen: various build fixes]
[sheng: fix control register breakage]
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NSheng Yang <sheng@linux.intel.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>