libipt: return -pte_internal for NULL pointers in internal interfaces

Change-Id: I377b56ff9c957bafe04422f82d35f6adfd341f50
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
libipt: add new errors for non-available timing and cbr information

Both pt_time_query_tsc() and pt_time_query_cbr() return zero if no timing or
cbr information is available.  Change this to an error.

Change unit tests to use queries instead of inspecting the internal state.

Change-Id: Ic7625ed5c15a67c340aad6ec843414888b07106f
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>