Performance metric numbers are calculated the following way :

   - out of the 256 bytes long OA reports, we accumulate the deltas
     into an array of uint64_t

   - the equations' generated code reads the accumulated uint64_t
     deltas and normalizes them for a particular platform

Our hardware is such that a number of counters in the OA reports
always return the same values (i.e. they're not programmable), and
they return the same values even across generations, and as a result a
number of equations are identical in different metric sets across
different generations.

Up to now we've kept the generated code of the equations separated in
different files (per generation/GT), and didn't apply any
factorization of the common equations. We could have make some
improvement by reusing equations within a given metrics file, but we
can go even further and reuse across generations (i.e. all files).

This change changes the code generation to emit a single file in which
we reuse equations emitted code based on the hash of equations'
strings.

Here are the savings in a meson build :

Before(.old)/after :
   $ du -h ./build/src/mesa/drivers/dri/libmesa_dri_drivers.so ./build/src/mesa/drivers/dri/libmesa_dri_drivers.so.old
   43M	./build/src/mesa/drivers/dri/libmesa_dri_drivers.so
   47M	./build/src/mesa/drivers/dri/libmesa_dri_drivers.so.old

   $ size build/src/mesa/drivers/dri/libmesa_dri_drivers.so build/src/mesa/drivers/dri/libmesa_dri_drivers.so.old
       text   data          bss	     dec            hex filename
   13054002 409424	 671856	14135282	 d7aff2	build/src/mesa/drivers/dri/libmesa_dri_drivers.so
   14550386 409552	 671856	15631794	 ee85b2	build/src/mesa/drivers/dri/libmesa_dri_drivers.so.old

As a side comment here is the size of the drivers if we remove all of
the metrics from the build :

   $ du -sh build/src/mesa/drivers/dri/libmesa_dri_drivers.so
   40M	build/src/mesa/drivers/dri/libmesa_dri_drivers.so

v2: Fix an issue with hashing of counter equations (Lionel)
    Build system rework (Emil)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com> (build system part)
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>