freedreno/ir3: Implement lowering passes for VS and GS

This introduces two new lowering passes. One to lower VS to explicit
outputs using STLW and one to lower GS to load input using LDLW and
implement the GS specific functionality.

Signed-off-by: Kristian H. Kristensen <hoegsberg@google.com>

src/compiler/shader_enums.c

@@ -254,6 +254,7 @@ gl_system_value_name(gl_system_value sysval)
      ENUM(SYSTEM_VALUE_BARYCENTRIC_SAMPLE),
      ENUM(SYSTEM_VALUE_BARYCENTRIC_CENTROID),
      ENUM(SYSTEM_VALUE_BARYCENTRIC_SIZE),
+     ENUM(SYSTEM_VALUE_GS_HEADER_IR3),
    };
    STATIC_ASSERT(ARRAY_SIZE(names) == SYSTEM_VALUE_MAX);
    return NAME(sysval);