perf/x86/intel/pt: Export pt_cap_get()

pt_cap_get() is required by the upcoming PT support in KVM guests.

Export it and move the capabilites enum to a global header.

As a global functions, "pt_*" is already used for ptrace and
other things, so it makes sense to use "intel_pt_*" as a prefix.

Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
Signed-off-by: Luwei Kang <luwei.kang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>