Create CPUDIR variable

The CPUDIR variable points to the location of a target's CPU directory.
Currently, it is set to cpu/$CPU.  However, using $CPUDIR will allow for
more flexibility in the future.  It lays the groundwork for reorganizing
U-Boot's directory structure to support a layout such as:

  arch/$ARCH/cpu/$CPU/* (architecture with multiple CPU types)
  arch/$ARCH/cpu/*      (architecture with one CPU type)

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/lib_blackfin/config.mk b/lib_blackfin/config.mk
index 1b5cbba..3ecade9 100644
--- a/lib_blackfin/config.mk
+++ b/lib_blackfin/config.mk
@@ -56,7 +56,7 @@
 
 LDR_FLAGS += --bmode $(subst BFIN_BOOT_,,$(CONFIG_BFIN_BOOT_MODE))
 LDR_FLAGS += --use-vmas
-LDR_FLAGS += --initcode $(obj)cpu/$(CPU)/initcode.o
+LDR_FLAGS += --initcode $(obj)$(CPUDIR)/initcode.o
 ifneq ($(CONFIG_BFIN_BOOT_MODE),BFIN_BOOT_UART)
 LDR_FLAGS-$(CONFIG_ENV_IS_EMBEDDED_IN_LDR) += \
 	--punchit $$(($(CONFIG_ENV_OFFSET))):$$(($(CONFIG_ENV_SIZE))):$(obj)env-ldr.o