Increase sanity around qemu-kvm

 * Depend on arch-appropriate qemu-system package.
 * Depend on ${binary:Version} of same.
 * Also build on arm64, x32, ppc64, ppc64el
 * Stop building on sparc for ubuntu.
Install /usr/bin/kvm wrapper for non 32-bit power.

32-bit power is a special snowflake to follow.
Handle 32-bit powerpc.

(From Adam and Ben on IRC).