intel/perf: Destination array calculation into function

intel/perf: Destination array calculation into function

Cuts 119 KiB from iris_dri.so and libvulkan_intel.so.

   text    data     bss     dec     hex filename
 917511       0       0  917511   e0007 meson-generated_.._intel_perf_metrics.c.o (before)
 796986       0       0  796986   c293a meson-generated_.._intel_perf_metrics.c.o (after)

   text    data     bss     dec     hex filename
14130948 365708  210004 14706660 e067e4 iris_dri.so (before)
14009332 365708  210004 14585044 de8cd4 iris_dri.so (after)

   text    data     bss     dec     hex filename
8124225  214264   22820 8361309  7f955d libvulkan_intel.so (before)
8002609  214264   22820 8239693  7dba4d libvulkan_intel.so (after)

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15237>