nb/intel/haswell: Handle boards that do not support IGD

Processor graphics is disabled on, for example, the C222 and C224
chipsets.

The change to resource assignment in northbridge.c prevents the following
warning that occurs when the IGD is disabled:

> skipping PCI: 00:00.0@3 fixed resource, size=0!

Tested on a Supermicro X10SLM+-F, which has the IGD disabled by the
chipset. The graphics memory is reclaimed and no issues were observed.

Also tested on an ASRock H81M-HDS. This board has an IGD, but no
regressions were observed.

Change-Id: I86d4aef50b6588f08b86c9758a4b95ccd65e9a96
Signed-off-by: Tristan Corrick <tristan@corrick.kiwi>
Reviewed-on: https://review.coreboot.org/c/30271
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
diff --git a/src/northbridge/intel/haswell/northbridge.c b/src/northbridge/intel/haswell/northbridge.c
index a803e98..fcdb683 100644
--- a/src/northbridge/intel/haswell/northbridge.c
+++ b/src/northbridge/intel/haswell/northbridge.c
@@ -371,13 +371,15 @@
 			  IORESOURCE_STORED | IORESOURCE_RESERVE |
 			  IORESOURCE_ASSIGNED | IORESOURCE_CACHEABLE;
 
-	/* BGSM -> TOLUD */
-	resource = new_resource(dev, index++);
-	resource->base = mc_values[BGSM_REG];
-	resource->size = mc_values[TOLUD_REG] - resource->base;
-	resource->flags = IORESOURCE_MEM | IORESOURCE_FIXED |
-			  IORESOURCE_STORED | IORESOURCE_RESERVE |
-			  IORESOURCE_ASSIGNED;
+	/* BGSM -> TOLUD. If the IGD is disabled, BGSM can equal TOLUD */
+	if (mc_values[BGSM_REG] != mc_values[TOLUD_REG]) {
+		resource = new_resource(dev, index++);
+		resource->base = mc_values[BGSM_REG];
+		resource->size = mc_values[TOLUD_REG] - resource->base;
+		resource->flags = IORESOURCE_MEM | IORESOURCE_FIXED |
+				  IORESOURCE_STORED | IORESOURCE_RESERVE |
+				  IORESOURCE_ASSIGNED;
+	}
 
 	/* 4GiB -> TOUUD */
 	base_k = 4096 * 1024; /* 4GiB */