Merge changes from topic "unify-qemu-machines" into integration

* changes:
  refactor(qemu): handle SPM_MM builds
  refactor(qemu): handle AArch64 flags
  refactor(qemu): common cpu features enablement
  refactor(qemu): common BL31 sources
  refactor(qemu): common BL1/2 sources
  refactor(qemu): move CPU definitions into one place
  refactor(qemu): move FDT stuff into one place