powerpc: Make KVM_GUEST default to n

KVM_GUEST adds a 1 MB array to the kernel (kvm_tmp) which grew
my kernel enough to cause it to fail to boot.

Dynamically allocating or reducing the size of this array is a
good idea, but in the meantime I think it makes sense to make
KVM_GUEST default to n in order to minimise surprises.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/Kconfig

@@ -24,7 +24,7 @@ source "arch/powerpc/platforms/wsp/Kconfig"
 
 config KVM_GUEST
 	bool "KVM Guest support"
-	default y
+	default n
 	---help---
 	  This option enables various optimizations for running under the KVM
 	  hypervisor. Overhead for the kernel when not running inside KVM should