Both, the legacy 'redqueen' trace via libxdc callback as well as new
dump_pt trace option are now toggled with aux-buffer trace_mode option.
This new qemu cmdline option allows to re-enable the old trace method,
or even use both trace methods at the same time.
libxdc does not create a bitmap in trace mode
This patch lets qemu create the bitmap instead
Note that the bitmap not compatible with libxdc bitmap since the trace
callback behavior is different.
