OS X Hypervisor.framework support in QEMU

These sources (and ../hvf-all.c) are adapted from Veertu Inc's vdhh (Veertu Desktop Hosted Hypervisor) (last known location: https://github.com/veertuinc/vdhh) with some minor changes, the most significant of which were:

  1. Adapt to our current QEMU's CPUState structure and address_space_rw API; many struct members have been moved around (emulated x86 state, xsave_buf) due to historical differences + QEMU needing to handle more emulation targets.
  2. Removal of apic_page and hyperv-related functionality.
  3. More relaxed use of qemu_mutex_lock_iothread.