egl: convert to use the common logging infrastructure
Related to #6828
As _eglLog also provides a fatal error level, this mr adds a fatal error level to common logging infrastructure for consistency.
egl_dri2.c uses loader_set_logger which is defined by the src/loader interface.
I haven't figured out how should (if ever) src/loader be modified as loader_logger is quite incompatible with mesa_log that has an additional tag parameter.