KVM: x86: handle idiv overflow at kvm_write_tsc

Its possible that idivl overflows (due to large delta stored in usdiff,
valid scenario).

Create an exception handler to catch the overflow exception (division by zero
is protected by vcpu->arch.virtual_tsc_khz check), and interpret it accordingly
(delta is larger than USEC_PER_SEC).

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=969644



Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>