target/ppc: POWER10 supports scv

This must have slipped through the cracks between adding POWER10 support
and scv support.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Message-Id: <20210415054227.1793812-3-npiggin@gmail.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>