nir: fill outputs_read field and add patch outputs read (v2)

This is to be used for TCS optimisations on radv.

v2: don't set written on reads (nha)

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/shader_info.h

@@ -66,6 +66,8 @@ typedef struct shader_info {
    uint32_t patch_inputs_read;
    /* Which patch outputs are actually written */
    uint32_t patch_outputs_written;
+   /* Which patch outputs are read */
+   uint32_t patch_outputs_read;
 
    /* Whether or not this shader ever uses textureGather() */
    bool uses_texture_gather;