feat:Increase default phase width

* To 20 bits

hdl/pkg_pscgen.vhd

 package pkg_pscgen is
 
-    constant C_W_PHASE   : natural := 15;
+    constant C_W_PHASE   : natural := 20;
     constant C_W_TIDX    : natural := 8;
     constant C_W_SINE    : natural := 26;
     constant C_W_SIG     : natural := 16;