The QMP command, like the interrupt reinjection logic it's connected
to, is only implemented in QEMU when TARGET_I386 is defined, so
checking for its availability on any other architecture is pointless.

On the other hand, when we're on x86, we shouldn still make sure that
rtc-reset-reinjection is available and refuse to set the time
otherwise.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1211938