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/common/v3d_limits.h

@@ -31,6 +31,7 @@
 
 #define V3D_MAX_FS_INPUTS 64
 #define V3D_MAX_VS_INPUTS 64
+#define V3D_MAX_ANY_STAGE_INPUTS MAX2(V3D_MAX_VS_INPUTS, V3D_MAX_FS_INPUTS)
 
 /* Not specifically a hardware limit, just coordination between compiler and
  * driver.