device/dram/ddr3: improve XMP support

- Fix offsets for supported CAS latencies
- Add support for reading CWL and CMD rate from the profile

Change-Id: Ie4f545ed1df92c146be02f56fea0ca9037478649
Signed-off-by: Dan Elkouby <streetwalkermc@gmail.com>
Reviewed-on: https://review.coreboot.org/25663
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/include/device/dram/ddr3.h

@@ -162,6 +162,8 @@ typedef struct dimm_attr_st {
 	u32 tWTR;
 	u32 tRTP;
 	u32 tFAW;
+	u32 tCWL;
+	u16 tCMD;
 
 	u8 reference_card;
 	/* XMP: Module voltage in mV */