x86_64: disable srat when numa emulation succeeds

When NUMA emulation succeeds, acpi_numa needs to be set to -1 so that
srat_disabled() will always return true.  We won't be calling
acpi_scan_nodes() or registering the true nodes we've found.

[hugh@veritas.com: Fix x86_64 CONFIG_NUMA_EMU build: acpi_numa needs CONFIG_ACPI_NUMA]
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Len Brown <lenb@kernel.org>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>