Commit 83f338f7 broke x86 hardware breakpoint emulation by moving the
debug exception handling out of cpu_exec. Fix this by moving all TCG
related bits back, only leaving the generic guest debugging parts in
cpus.c.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
CC: TeLeMan <geleman@gmail.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>