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

lib/rfnoc/blocks/rfnoc_block_fft/rfnoc_block_fft_tb.sv

@@ -30,6 +30,7 @@ module rfnoc_block_fft_tb();
   // Block configuration
   localparam int NOC_ID        = 32'hFF70_0000;
   localparam int CHDR_W        = 64;
+  localparam int SAMP_W        = 32;
   localparam int THIS_PORTID   = 'h123;
   localparam int MTU           = 10;
   localparam int NUM_PORTS     = 1;
@@ -60,6 +61,8 @@ module rfnoc_block_fft_tb();
   // Bus Functional Models
   //---------------------------------------------------------------------------
 
+  typedef ChdrData #(CHDR_W, SAMP_W)::chdr_word_t chdr_word_t;
+
   RfnocBackendIf        backend            (rfnoc_chdr_clk, rfnoc_ctrl_clk);
   AxiStreamIf #(32)     m_ctrl             (rfnoc_ctrl_clk, 1'b0);
   AxiStreamIf #(32)     s_ctrl             (rfnoc_ctrl_clk, 1'b0);