powerpc: Always enable queued spinlocks for 64s, disable for others

Queued spinlocks have shown to have good performance and fairness
properties even on smaller (2 socket) POWER systems. This selects them
automatically for 64s. For other platforms they are de-selected, the
standard spinlock is far simpler and smaller code, and single chips
with a handful of cores is unlikely to show any improvement.

CONFIG_EXPERT still allows this to be changed, e.g., to help debug
performance or correctness issues.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210118123451.1452206-1-npiggin@gmail.com