arch/tile: parameterize system PLs to support KVM port

While not a port to KVM (yet), this change modifies the kernel
to be able to build either at PL1 or at PL2 with a suitable
config switch.  Pushing up this change avoids handling branch
merge issues going forward with the KVM work.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
diff --git a/arch/tile/kernel/traps.c b/arch/tile/kernel/traps.c
index 0f362dc..7826a8b1 100644
--- a/arch/tile/kernel/traps.c
+++ b/arch/tile/kernel/traps.c
@@ -278,7 +278,7 @@
 	case INT_DOUBLE_FAULT:
 		/*
 		 * For double fault, "reason" is actually passed as
-		 * SYSTEM_SAVE_1_2, the hypervisor's double-fault info, so
+		 * SYSTEM_SAVE_K_2, the hypervisor's double-fault info, so
 		 * we can provide the original fault number rather than
 		 * the uninteresting "INT_DOUBLE_FAULT" so the user can
 		 * learn what actually struck while PL0 ICS was set.