drivers/net/npe: descend only when CONFIG_IXP4XX_NPE=y

CONFIG_IXP4XX_NPE is defined only for CPU ixp.
It is not necessary to filter by CPU ixp.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/drivers/net/npe/Makefile b/drivers/net/npe/Makefile
index 7fa5ea6..e36c0bb 100644
--- a/drivers/net/npe/Makefile
+++ b/drivers/net/npe/Makefile
@@ -10,7 +10,7 @@
 CPPFLAGS  += $(LOCAL_CFLAGS) # needed for depend
 HOSTCFLAGS  += $(LOCAL_CFLAGS)
 
-obj-$(CONFIG_IXP4XX_NPE) := npe.o \
+obj-y := npe.o \
 	miiphy.o \
 	IxOsalBufferMgt.o \
 	IxOsalIoMem.o \