nb/intel/sandybridge: Lower tPRPDEN to 1

This is the default value, and matches what vendor firmware does.

Change-Id: Id0c9758a845d711a87c4b06f89fa0926ae658e02
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47745
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/northbridge/intel/sandybridge/raminit_common.c

@@ -175,7 +175,7 @@ void dram_timing_regs(ramctr_timing *ctrl)
 		.tXP     = ctrl->tXP,
 		.tAONPD  = ctrl->tAONPD,
 		.tCPDED  = 2,
-		.tPRPDEN = 2,
+		.tPRPDEN = 1,
 	};
 
 	/*