target/ppc: Fix THREAD_SIBLING_FOREACH for multi-socket

target/ppc: Fix THREAD_SIBLING_FOREACH for multi-socket

The THREAD_SIBLING_FOREACH macro wasn't excluding threads from other
chips. Add chip_index field to the thread state and add a check for the
new field in the macro.

Fixes: b769d4c8f4c6 ("target/ppc: Add initial flags and helpers for SMT support")
Signed-off-by: Glenn Miles <milesg@linux.ibm.com>
[npiggin: set chip_index for spapr too]
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>