Make vcpu_ioctl() a macro wrapper and pretty the _name_ of the ioctl on
failure instead of the number.  Add inner macros to allow handling cases
where the name of the ioctl needs to be resolved higher up the stack, and
to allow using the formatting for non-ioctl syscalls without being
technically wrong.

Deliberately do not use __stringify(), as that will expand the ioctl all
the way down to its numerical sequence, again the intent is to print the
name of the macro.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>