device/dram/ddr2: Add common ddr2 spd decoder

Decode DDR2 SPD similar to DDR3 SPD decoder to ease
readability, reduce code complexity and reduce size of
maintainable code.

Rename dimm_is_registered to spd_dimm_is_registered_ddr3 to avoid
compilation errors.

Change-Id: I741f0e61ab23e3999ae9e31f57228ba034c2509e
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/18273
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins)
diff --git a/src/northbridge/via/vx900/raminit_ddr3.c b/src/northbridge/via/vx900/raminit_ddr3.c
index 4878571..2de7734 100644
--- a/src/northbridge/via/vx900/raminit_ddr3.c
+++ b/src/northbridge/via/vx900/raminit_ddr3.c
@@ -703,7 +703,7 @@
 	pci_mod_config8(MCU, 0x6b, 0x80, 0x00);
 
 	/* Step 8 - If we have registered DIMMs, we need to set bit[0] */
-	if (dimm_is_registered(ctrl->dimm_type)) {
+	if (spd_dimm_is_registered_ddr3(ctrl->dimm_type)) {
 		printram("Enabling RDIMM support in memory controller\n");
 		pci_mod_config8(MCU, 0x6c, 0x00, 0x01);
 	}