device/ddr2,ddr3: Rename and move a few things

In order for ddr2.h and ddr3.h to be included in the same file it
cannot have conflicting definitions, therefore rename a few things and
move some things to a common header.

Change-Id: I6056148872076048e055f1d20a60ac31afd7cde6
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/23717
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>

src/northbridge/intel/i945/raminit.c

@@ -362,7 +362,7 @@ static void gather_common_timing(struct sys_info *sysinfo,
 
 	for (i = 0; i < (2 * DIMM_SOCKETS); i++) {
 		int device = get_dimm_spd_address(sysinfo, i), bytes_read;
-		struct dimm_attr_st dimm_info;
+		struct dimm_attr_ddr2_st dimm_info;
 
 		/* Initialize the socket information with a sane value */
 		sysinfo->dimm[i] = SYSINFO_DIMM_NOT_POPULATED;