Feature Request: Allow printfs to go to different file descriptors

Checklist

• Did you write out a description of the feature you want to see?
• Did you look around for any related features?
• Did you specify relevant external information?

Feature Description

When emitting printf, don’t hard-code the destination file descriptor to 80000002.

Instead use something like:

`ifndef PRINTF_FD
 `define PRINTF_FD 'h80000002.
`endif

Type of Feature

• backend code generation

Related Features

Yes this bit of code:

    def printf(str: StringLit, args: Seq[Expression]): Seq[Any] = {
      val strx = str.verilogEscape +: args.flatMap(Seq(",", _))
      Seq("$fwrite(32'h80000002,", strx, ");")
    }

External Information

[chick]

If this gets implemented it would be a good idea to update the following stackoverflow: Can chisel implement printf to a file?

[chick]

Noting related chisel issue: Can chisel implement printf to a file #1290