cputlb: move CPU_LOOP() for tlb_reset() to exec.c

To prepare for multi-arch, cputlb.c should only have awareness of one
single architecture. This means it should not have access to the full
CPU lists which may be heterogeneous. Instead, push the CPU_LOOP() up
to the one and only caller in exec.c.

Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Message-Id: <db06dc6c49f8970caaf116d0385f00ee10a56f2f.1441614289.git.crosthwaite.peter@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>