freedreno,tu: Don't request fragcoord components not being read.
For #2680 (closed).
Tested with dEQP-VK.glsl.builtin_var.simple.fragcoord_xyz/w dEQP-GLES2.functional.shaders.builtin_variable.fragcoord_xyz/w
For #2680 (closed).
Tested with dEQP-VK.glsl.builtin_var.simple.fragcoord_xyz/w dEQP-GLES2.functional.shaders.builtin_variable.fragcoord_xyz/w