features: fix listing for GL_ARB_parallel_shader_compile

this isn't actually all drivers
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <!12909>

docs/features.txt

@@ -301,7 +301,7 @@ Khronos, ARB, and OES extensions that are not part of any OpenGL or OpenGL ES ve
   GL_ARB_ES3_2_compatibility                            DONE (i965/gen8+, radeonsi, virgl, zink)
   GL_ARB_fragment_shader_interlock                      DONE (i965, zink)
   GL_ARB_gpu_shader_int64                               DONE (i965/gen8+, nvc0, radeonsi, softpipe, llvmpipe, zink)
-  GL_ARB_parallel_shader_compile                        DONE (all drivers)
+  GL_ARB_parallel_shader_compile                        DONE (freedreno, iris, radeonsi)
   GL_ARB_post_depth_coverage                            DONE (i965, nvc0, radeonsi, llvmpipe, zink)
   GL_ARB_robustness_isolation                           not started
   GL_ARB_sample_locations                               DONE (nvc0, zink)