KVM: x86: fix TRACE_INCLUDE_PATH and remove -I. header search paths

The header search path -I. in kernel Makefiles is very suspicious;
it allows the compiler to search for headers in the top of $(srctree),
where obviously no header file exists.

The reason of having -I. here is to make the incorrectly set
TRACE_INCLUDE_PATH working.

As the comment block in include/trace/define_trace.h says,
TRACE_INCLUDE_PATH should be a relative path to the define_trace.h

Fix the TRACE_INCLUDE_PATH, and remove the iffy include paths.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>