[MIPS] Use KBUILD_DEFCONFIG

With KBUILD_DEFCONFIG we don't have to ship a second copy of ip22_defconfig.
Signed-off-by: NAdrian Bunk <adrian.bunk@movial.fi>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/Makefile

@@ -12,6 +12,8 @@
 # for "archclean" cleaning up for this architecture.
 #
 
+KBUILD_DEFCONFIG := ip22_defconfig
+
 cflags-y :=
 
 #