[POWERPC] Don't include powerpc/sysdev/rom.o for arch/ppc builds

sysdev/rom.c is for arch/powerpc only.  Don't compile it when building
an arch/ppc kernel.
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Sylvain Munaut <tnt@246tNt.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/sysdev/Makefile

@@ -12,7 +12,6 @@ obj-$(CONFIG_MMIO_NVRAM)	+= mmio_nvram.o
 obj-$(CONFIG_FSL_SOC)		+= fsl_soc.o
 obj-$(CONFIG_TSI108_BRIDGE)	+= tsi108_pci.o tsi108_dev.o
 obj-$(CONFIG_QUICC_ENGINE)	+= qe_lib/
-obj-$(CONFIG_MTD)		+= rom.o
 
 ifeq ($(CONFIG_PPC_MERGE),y)
 obj-$(CONFIG_PPC_I8259)		+= i8259.o
@@ -21,5 +20,6 @@ endif
 
 # Temporary hack until we have migrated to asm-powerpc
 ifeq ($(ARCH),powerpc)
+obj-$(CONFIG_MTD)		+= rom.o
 obj-$(CONFIG_CPM2)		+= cpm2_common.o cpm2_pic.o
 endif