mpc83xx: fix undefined reference to `flush_cache' error in simpc8313 build

extend commit c70564e6b1bd08f3230182392238907f3531a87e
"NAND: Fix cache and memory inconsistency issue" to add the cache.o dependency
to the simpc8313 build and fix this:

...Large Page NAND...Configuring for SIMPC8313 board...
nand_boot_fsl_elbc.o: In function `nand_boot':
nand_spl/board/sheldon/simpc8313/nand_boot_fsl_elbc.c:150: undefined reference to `flush_cache'
make[1]: *** [/home/r1aaha/git/u-boot-mpc83xx/nand_spl/u-boot-spl] Error 1
make: *** [nand_spl] Error 2

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>

nand_spl/board/sheldon/simpc8313/Makefile

@@ -34,7 +34,8 @@ AFLAGS	+= -DCONFIG_NAND_SPL
 CFLAGS	+= -DCONFIG_NAND_SPL
 
 SOBJS	= start.o ticks.o
-COBJS	= nand_boot_fsl_elbc.o $(BOARD).o sdram.o ns16550.o nand_init.o time.o
+COBJS	= nand_boot_fsl_elbc.o $(BOARD).o sdram.o ns16550.o nand_init.o \
+	  time.o cache.o
 
 SRCS	:= $(addprefix $(obj),$(SOBJS:.o=.S) $(COBJS:.o=.c))
 OBJS	:= $(addprefix $(obj),$(SOBJS) $(COBJS))
@@ -78,6 +79,9 @@ $(obj)ns16550.c:
 $(obj)nand_init.c:
 	ln -sf $(SRCTREE)/cpu/mpc83xx/nand_init.c $<
 
+$(obj)cache.c:
+	ln -sf $(SRCTREE)/lib_ppc/cache.c $<
+
 $(obj)time.c:
 	ln -sf $(SRCTREE)/lib_ppc/time.c $<