r600/sfn: Lower *sign opcodes in nir

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6706>
diff --git a/src/gallium/drivers/r600/r600_pipe_common.c b/src/gallium/drivers/r600/r600_pipe_common.c
index 8965f27..43bad11 100644
--- a/src/gallium/drivers/r600/r600_pipe_common.c
+++ b/src/gallium/drivers/r600/r600_pipe_common.c
@@ -1186,6 +1186,8 @@
 	.lower_fpow = true,
 	.lower_fdiv = true,
 	.lower_idiv = true,
+        .lower_isign = true,
+        .lower_fsign = true,
 	.lower_fmod = true,
 	.lower_doubles_options = nir_lower_fp64_full_software,
 	.lower_int64_options = 0,