[POWERPC] Don't build arch/powerpc/sysdev/dcr.c for ARCH=ppc kernels

dcr.c is an arch/powerpc only thing.  Compiling ppc405 arch/ppc kernels
throws warnings without this change.
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

arch/powerpc/sysdev/Makefile

@@ -6,7 +6,6 @@ mpic-msi-obj-$(CONFIG_PCI_MSI)	+= mpic_msi.o mpic_u3msi.o
 obj-$(CONFIG_MPIC)		+= mpic.o $(mpic-msi-obj-y)
 
 obj-$(CONFIG_PPC_MPC106)	+= grackle.o
-obj-$(CONFIG_PPC_DCR)		+= dcr.o
 obj-$(CONFIG_PPC_DCR_NATIVE)	+= dcr-low.o
 obj-$(CONFIG_PPC_PMI)		+= pmi.o
 obj-$(CONFIG_U3_DART)		+= dart_iommu.o
@@ -33,6 +32,7 @@ endif
 ifeq ($(ARCH),powerpc)
 obj-$(CONFIG_CPM)		+= cpm_common.o
 obj-$(CONFIG_CPM2)		+= cpm2_common.o cpm2_pic.o
+obj-$(CONFIG_PPC_DCR)		+= dcr.o
 obj-$(CONFIG_8xx)		+= mpc8xx_pic.o commproc.o
 obj-$(CONFIG_UCODE_PATCH)	+= micropatch.o
 endif