MIPS: TXx9: Migrate to new platform makefile style.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/Kbuild.platforms b/arch/mips/Kbuild.platforms
index e0fb370..a4bda75 100644
--- a/arch/mips/Kbuild.platforms
+++ b/arch/mips/Kbuild.platforms
@@ -20,6 +20,7 @@
 platforms += sgi-ip32
 platforms += sibyte
 platforms += sni
+platforms += txx9
 platforms += vr41xx
 platforms += wrppmc