feat: add x prop checker module

rtl/utils/xchecker.sv

@@ -0,0 +1,18 @@
+
+`ifndef INC_XCHECKER_SV
+`define INC_XCHECKER_SV
+
+module xchecker #(
+    parameter DATA_WIDTH = 1
+) (
+    input logic                  clk_i,
+    input logic [DATA_WIDTH-1:0] dat_i
+);
+
+  XCHECKER :
+  assert property (@(posedge clk_i) ((^(dat_i)) !== 1'bx))
+  else
+    $fatal("\n [error]: detected x value here which can lead to the x state propagation problem\n");
+
+endmodule
+`endif