sim: Parameterize chdr_word_t data type

This replaces chdr_word_t, which was a statically defined 64-bit data
type, with a paramaterizable data type that matches the defined CHDR_W.
Code that formerly referenced the chdr_word_t data type can now define
the data type for their desired CHDR_W and ITEM_W as follows:

  // Define the CHDR word and item/sample data types
  typedef ChdrData #(CHDR_W, ITEM_W)::chdr_word_t chdr_word_t;
  typedef ChdrData #(CHDR_W, ITEM_W)::item_t      item_t;

ITEM_W is optional when defining chdr_word_t if items are not
needed. Static methods in the ChdrData class also provide the ability to
convert between CHDR words and data items. For example:

  // Convert CHDR data buffer to a buffer of samples
  samples = ChdrData#(CHDR_W, ITEM_W)::chdr_to_item(data);


Original-commit: fc895feacb8dde3b02c9a4eccb4b4f4a654f2881

sim/rfnoc/PkgAxisCtrlBfm.sv

@@ -29,7 +29,7 @@ package PkgAxisCtrlBfm;
     //------------
 
     axis_ctrl_header_t header;
-    chdr_word_t        timestamp;
+    chdr_timestamp_t   timestamp;
     ctrl_op_word_t     op_word;
     ctrl_word_t        data[$];
 
@@ -86,7 +86,7 @@ package PkgAxisCtrlBfm;
       ref axis_ctrl_header_t header,
       ref ctrl_op_word_t     op_word,
       ref ctrl_word_t        data[$],
-      input chdr_word_t      timestamp = 0
+      input chdr_timestamp_t timestamp = 0
     );
       this.header    = header;
       this.data      = data;