[pinmux] Add block level synth setup

Signed-off-by: Timothy Chen <timothytim@google.com>
diff --git a/hw/ip/pinmux/pinmux.core b/hw/ip/pinmux/pinmux.core
index e32e3b8..3c5a364 100644
--- a/hw/ip/pinmux/pinmux.core
+++ b/hw/ip/pinmux/pinmux.core
@@ -34,4 +34,11 @@
         verilator_options:
           - "-Wall"
 
-
+  syn:
+    <<: *default_target
+    # TODO: set default to DC once
+    # this option is available
+    # olofk/edalize#89
+    default_tool: icarus
+    parameters:
+      - SYNTHESIS=true