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/Makefile b/arch/tile/Makefile
index a700f7f..17acce7 100644
--- a/arch/tile/Makefile
+++ b/arch/tile/Makefile
@@ -53,6 +53,8 @@
 # See arch/tile/Kbuild for content of core part of the kernel
 core-y		+= arch/tile/
 
+core-$(CONFIG_KVM) += arch/tile/kvm/
+
 ifdef TILERA_ROOT
 INSTALL_PATH ?= $(TILERA_ROOT)/tile/boot
 endif