[MIPS] Use KBUILD_DEFCONFIG

With KBUILD_DEFCONFIG we don't have to ship a second copy of ip22_defconfig.

Signed-off-by: Adrian Bunk <adrian.bunk@movial.fi>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index 3fb7f30..72097da 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -12,6 +12,8 @@
 # for "archclean" cleaning up for this architecture.
 #
 
+KBUILD_DEFCONFIG := ip22_defconfig
+
 cflags-y :=
 
 #