Fix handling of qemu config files from previous commit
    
    The /etc/qemu directory is potentially used by any of the QEMU
    sub RPMs, so needs to be in qemu-common.
    
    The qemu-system-x86  sub-RPM should always include target-x86_64.conf
    regardless host arch, since it can be used by both the TCG and KVM
    binaries.