compiler: tidy up double_inputs_read uses

First we move double_inputs_read into a vs struct in the union,
double_inputs_read is only used for vs inputs so this will
save space and also allows us to add a new double_inputs field.

We add the new field because c2acf97fcc changed the behaviour
of double_inputs_read, and while it's no longer used to track
actual reads in i965 we do still want to track this for gallium
drivers.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/compiler/shader_info.h

@@ -67,8 +67,6 @@ typedef struct shader_info {
 
    /* Which inputs are actually read */
    uint64_t inputs_read;
-   /* Which inputs are actually read and are double */
-   uint64_t double_inputs_read;
    /* Which outputs are actually written */
    uint64_t outputs_written;
    /* Which outputs are actually read */
@@ -109,6 +107,14 @@ typedef struct shader_info {
    bool has_transform_feedback_varyings;
 
    union {
+      struct {
+         /* Which inputs are doubles */
+         uint64_t double_inputs;
+
+         /* Which inputs are actually read and are double */
+         uint64_t double_inputs_read;
+      } vs;
+
       struct {
          /** The number of vertices recieves per input primitive */
          unsigned vertices_in;