arch/tile: prefer "tilepro" as the name of the 32-bit architecture

With this change, you can (and should) build with ARCH=tilepro for the
current 32-bit chips.  Building with ARCH=tile continues to work, but
we've renamed the defconfig file to tilepro_defconfig for consistency.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
diff --git a/Makefile b/Makefile
index 3dcca28..cadf4cd 100644
--- a/Makefile
+++ b/Makefile
@@ -221,6 +221,9 @@
 endif
 
 # Additional ARCH settings for tile
+ifeq ($(ARCH),tilepro)
+       SRCARCH := tile
+endif
 ifeq ($(ARCH),tilegx)
        SRCARCH := tile
 endif