aux/trace: print enum names instead of integer values in gallium traces

Having only magic constants instead of human-readable strings in traces not only hinders readability, but also may affect trace comparision of old and new traces if new enums have been added or modified (thus possibly changing the values of existing ones.)

So we implement printing of enum names as strings instead. In order to have those strings, we need to add some new helper functions, which we generate from pipe/p_definitions.h header via a script.