Add directory that will contain SystemRDL files for tests

tests/.gitignore

@@ -0,0 +1,2 @@
+srdl2sv_out
+*.fst

tests/systemrdl/simple_rw_reg.rdl

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+addrmap simple_rw_reg {
+    reg {
+        field {sw=rw; hw=rw;} f1 [15:0];
+        field {sw=rw; hw=rw;} f2 [31:16];
+    } register_0 [2];
+};