vc/amd/agesa/[...]/Config: Avoid out-of-bounds warnings

The memNTrainFlowControl array is generating Coverity warnings
in multiple places in code where it attempts to write to index 1.
The array is defined as either 2 elements or 1 of NULL depending
on #if (AGESA_ENTRY_INIT_POST == TRUE). This is likely a false
alarm from Coverity (memory should not be training outside of a
POST), but adding a second NULL element for the
AGESA_ENTRY_INIT_POST == FALSE case. Tested on Lenovo G505s.

Change-Id: Iaebe0830471e1854d6191c69cdaa552f900ba7a6
Signed-off-by: Joe Moore <awokd@danwin1210.me>
Found-by: Coverity CID 1357451, 1357452, 1357453
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38176
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/vendorcode/amd/agesa/f14/Config/OptionMemoryInstall.h

@@ -680,7 +680,8 @@ BOOLEAN MemFS3DefConstructorRet (
    *---------------------------------------------------------------------------------------------------
    */
   OPTION_MEM_FEATURE_NB* memNTrainFlowControl[] = {    // Training flow control
-    NULL
+    NULL,
+    NULL,
   };
   /*---------------------------------------------------------------------------------------------------
    * DEFAULT TECHNOLOGY BLOCK

src/vendorcode/amd/agesa/f15tn/Config/OptionMemoryInstall.h

@@ -4662,7 +4662,8 @@ BOOLEAN MemFS3DefConstructorRet (
    *---------------------------------------------------------------------------------------------------
    */
   OPTION_MEM_FEATURE_NB* memNTrainFlowControl[] = {    // Training flow control
-    NULL
+    NULL,
+    NULL,
   };
   /*---------------------------------------------------------------------------------------------------
    * DEFAULT TECHNOLOGY BLOCK

src/vendorcode/amd/agesa/f16kb/Config/OptionMemoryInstall.h

@@ -1531,7 +1531,8 @@ BOOLEAN MemFS3DefConstructorRet (
    *---------------------------------------------------------------------------------------------------
    */
   OPTION_MEM_FEATURE_NB* memNTrainFlowControl[] = {    // Training flow control
-    NULL
+    NULL,
+    NULL,
   };
   /*---------------------------------------------------------------------------------------------------
    * DEFAULT TECHNOLOGY BLOCK