Add proper SPD definitions for DDR1/2/3

Also adds helper functions for DDR1/2 to verify the checksum.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/common/Makefile b/common/Makefile
index 7811032..944b1c0 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -151,6 +151,7 @@
 COBJS-$(CONFIG_CMD_MFSL) += cmd_mfsl.o
 COBJS-$(CONFIG_MP) += cmd_mp.o
 COBJS-$(CONFIG_CMD_SF) += cmd_sf.o
+COBJS-$(CONFIG_DDR_SPD) += ddr_spd.o
 
 COBJS	:= $(COBJS-y)
 SRCS	:= $(AOBJS:.o=.S) $(COBJS:.o=.c)