target/ppc: Big-core scratch register fix

target/ppc: Big-core scratch register fix

The per-core SCRATCH0-7 registers are shared between big cores, which
was missed in the big-core implementation. It is difficult to model
well with the big-core == 2xPnvCore scheme we moved to, this fix
uses the even PnvCore to store the scrach data.

Also remove a stray log message that came in with the same patch that
introduced patch.

Fixes: c26504afd5f5c ("ppc/pnv: Add a big-core mode that joins two regular cores")
Cc: qemu-stable@nongnu.org
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>