Fix a bug in libvmmapi 'vm_copy_setup()' where it would return success even if
the 'gpa' was in the guest MMIO region. This would manifest as a segmentation
fault in 'vm_map_copyin()' or 'vm_map_copyout()' because 'vm_map_gpa()' would
return NULL for this 'gpa'.

Fix this by calling 'vm_map_gpa()' in 'vm_copy_setup' and returning a failure
if the 'gpa' cannot be mapped. This matches the behavior of 'vm_copy_setup()'
in vmm.ko.

MFC after: 1 week