v3d: rename vertex shader key (num)_fs_inputs fields

Until now this made sense because we always paired vertex shaders
with fragment shaders, but as soon as we implement geometry and
tessellation shaders that will no longer be the case, so rename
this to (num_)used_outputs.

v2: Use 'used_outputs' instead of ns_outputs, which is more explicit (Eric).

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/broadcom/compiler/v3d_compiler.h

@@ -374,8 +374,8 @@ struct v3d_fs_key {
 struct v3d_vs_key {
         struct v3d_key base;
 
-        struct v3d_varying_slot fs_inputs[V3D_MAX_FS_INPUTS];
-        uint8_t num_fs_inputs;
+        struct v3d_varying_slot used_outputs[V3D_MAX_ANY_STAGE_INPUTS];
+        uint8_t num_used_outputs;
 
         bool is_coord;
         bool per_vertex_point_size;