Perfetto integration

Hi, this is an attempt at integrating Perfetto and gfx-pps in Mesa, ready to be reviewed properly.

• mesa-dev discussion
• related issue #4262

TODO list:

• Perfetto SDK is included with a meson wrap.
• gfx-pps v0.3.0 is added in src/tool/pps as both a library and an executable (a Perfetto producer advertising a "gpu" data-source).
  • pps-config tool useful for querying available devices and counters.
• Driver specific code used by the data-source can be listed under src/<driver>/ds/pps_driver_<driver>.cc and included by gfx-pps at meson configuration time.
  • Panfrost pps driver !10215 (merged)
  • Intel pps driver !10216 (merged)
  • Freedreno pps driver !9901 (merged)
• Documentation at docs/pps.rst
• Provide some perfetto .cfg examples for GPU tracing.