target-ppc: Give a meaningful error if too many threads are specified

target-ppc: Give a meaningful error if too many threads are specified

Currently the target-ppc tcg code only supports a single thread.  You can
specify more, but they're treated identically to multiple cores.  On KVM
we obviously can't support more threads than the hardware; if more are
specified it will cause strange and cryptic errors.

This patch clarifies the situation by giving a simple meaningful error if
more threads are specified than we can support.

Signed-off-by: Mike Qiu <[email protected]>
Signed-off-by: David Gibson <[email protected]>
Signed-off-by: Alexander Graf <[email protected]>