i965: Select ranges of UBO data to be uploaded as push constants.

This adds a NIR pass that decides which portions of UBOS we should
upload as push constants, rather than pull constants.

v2: Switch to uint16_t for the UBO block number, because we may
    have a lot of them in Vulkan (suggested by Jason).  Add more
    comments about bitfield trickery (requested by Matt).

v3: Skip vec4 stages for now...I haven't finished wiring up support
    in the vec4 backend, and so pushing the data but not using it
    will just be wasteful.

Reviewed-by: Matt Turner <mattst88@gmail.com>

src/intel/compiler/brw_compiler.h

@@ -468,6 +468,13 @@ struct brw_image_param {
  */
 #define BRW_SHADER_TIME_STRIDE 64
 
+struct brw_ubo_range
+{
+   uint16_t block;
+   uint8_t start;
+   uint8_t length;
+};
+
 struct brw_stage_prog_data {
    struct {
       /** size of our binding table. */
@@ -488,6 +495,8 @@ struct brw_stage_prog_data {
       /** @} */
    } binding_table;
 
+   struct brw_ubo_range ubo_ranges[4];
+
    GLuint nr_params;       /**< number of float params/constants */
    GLuint nr_pull_params;
    unsigned nr_image_params;