[pcbios] Merge adjacent memory regions of same type

Some BIOSes can report multiple memory regions which may be adjacent
and the same type.  Since only the first region is used in the
mboot.c32 layer it's possible to run out of memory when loading all of
the boot modules.  One may get around this problem by having iPXE
merge these memory regions internally.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/firmware/pcbios/memmap.c

  */
 static int meme820 ( struct memory_map *memmap ) {
 	struct memory_region *region = memmap->regions;
+	struct memory_region *prev_region = NULL;
 	uint32_t next = 0;
 	uint32_t smap;
 	size_t size;
 
 		region->start = e820buf.start;
 		region->end = e820buf.start + e820buf.len;
-		region++;
-		memmap->count++;
+
+		/* Check for adjacent regions and merge them */
+		if ( prev_region && ( region->start == prev_region->end ) ) {
+			prev_region->end = region->end;
+		} else {
+			prev_region = region;
+			region++;
+			memmap->count++;
+		}
 
 		if ( memmap->count >= ( sizeof ( memmap->regions ) /
 					sizeof ( memmap->regions[0] ) ) ) {