arch-x86: Stop printing a source operand for the monitor instruction.
arch-x86: Stop printing a source operand for the monitor instruction.

Like CPUID, all operands for this instruction are implicit and are not
written out when putting it into assembly. Stop printing a source
operand when generating disassembly in gem5.

Change-Id: I95898afdd9101ad393b3aace99536db602752a64
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49225
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Maintainer: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5