gallium/util: add util_format_is_srgb() helper

src/gallium/auxiliary/util/u_format.h

@@ -410,6 +410,13 @@ util_format_is_s3tc(enum pipe_format format)
    return desc->layout == UTIL_FORMAT_LAYOUT_S3TC ? TRUE : FALSE;
 }
 
+static INLINE boolean 
+util_format_is_srgb(enum pipe_format format)
+{
+   const struct util_format_description *desc = util_format_description(format);
+   return desc->colorspace == UTIL_FORMAT_COLORSPACE_SRGB;
+}
+
 static INLINE boolean
 util_format_has_depth(const struct util_format_description *desc)
 {