intel/perf: rename gen_perf to gen_perf_config

intel/perf: rename gen_perf to gen_perf_config

This structure contains the configurations of the metrics for the
current platform, and the settings needed for the perf subsystem to
query that configuration from the device.  This data is available
without a rendering context, and needed to support MDAPI metrics for
Vulkan.

A gen_perf_context struct will be added later, which holds additional
state from the rendering context necessary for metric data
collection.  The gen_perf struct needs a more precise name to reduce
confusion.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>