icount: introduce cpu_get_icount_raw

Separate accessing the instruction counter from the compensation for
speed and halting that are introduced by qemu_icount_bias.  This
introduces new infrastructure used by the record/replay patches.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
