intel: Rename Genx keyword to Gfxx

Commands used to do the changes:
export SEARCH_PATH="src/intel src/gallium/drivers/iris src/mesa/drivers/dri/i965"
grep -E "Gen[[:digit:]]+" -rIl $SEARCH_PATH | xargs sed -ie "s/Gen\([[:digit:]]\+\)/Gfx\1/g"

Exclude changes in src/intel/perf/oa-*.xml:
find src/intel/perf -type f \( -name "*.xml" \) | xargs sed -ie "s/Gfx/Gen/g"

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9936>

src/intel/compiler/brw_nir.c

@@ -614,7 +614,7 @@ brw_nir_optimize(nir_shader *nir, const struct brw_compiler *compiler,
        *
        * Passing 1 to the peephole select pass causes it to convert
        * if-statements that contain at most a single ALU instruction (total)
-       * in both branches.  Before Gen6, some math instructions were
+       * in both branches.  Before Gfx6, some math instructions were
        * prohibitively expensive and the results of compare operations need an
        * extra resolve step.  For these reasons, this pass is more harmful
        * than good on those platforms.