compiler: add SYSTEM_VALUE_VARYING_COORD

Used internally in freedreno/ir3 for the vec2 value that hw passes to
shader to use as coordinate for bary.f (varying fetch) instruction.
This is not the same as SYSTEM_VALUE_FRAG_COORD.

Signed-off-by: Rob Clark <robdclark@gmail.com>

src/compiler/shader_enums.c

@@ -244,6 +244,7 @@ gl_system_value_name(gl_system_value sysval)
      ENUM(SYSTEM_VALUE_DEVICE_INDEX),
      ENUM(SYSTEM_VALUE_VIEW_INDEX),
      ENUM(SYSTEM_VALUE_VERTEX_CNT),
+     ENUM(SYSTEM_VALUE_VARYING_COORD),
    };
    STATIC_ASSERT(ARRAY_SIZE(names) == SYSTEM_VALUE_MAX);
    return NAME(sysval);