Dynamically get the number of child device in general definition block

The size of general definition block varies on different platform/machines.
In such case the number of child device is also different.
And it will be better to get the number of child device in general definition
block dynamically.

The number of child device can be calculated by the following formula:
	(block_size - block_header_size) /
		sizeof( struct child_device_config)

http://bugs.freedesktop.org/show_bug.cgi?id=20429

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>

src/bios_reader/bios_reader.c

@@ -170,6 +170,7 @@ static void dump_general_definitions(void)
     struct child_device_config *child;
     int i;
     char child_id[11];
+    int child_device_num;
 
     block = find_section(BDB_GENERAL_DEFINITIONS);
 
@@ -188,7 +189,8 @@ static void dump_general_definitions(void)
     printf("\tBoot display type: 0x%02x%02x\n", defs->boot_display[1],
 	   defs->boot_display[0]);
     printf("\tTV data block present: %s\n", YESNO(tv_present));
-    for (i = 0; i < 4; i++) {
+    child_device_num = (block->size - sizeof(*defs)) / sizeof(*child);
+    for (i = 0; i < child_device_num; i++) {
 	child = &defs->devices[i];
 	if (!child->device_type) {
 	    printf("\tChild device %d not present\n", i);

src/i830_bios.h

@@ -228,7 +228,7 @@ struct bdb_general_definitions {
 	 * TV and LVDS are missing, so be careful when interpreting
 	 * [4] and [5].
 	 */
-	struct child_device_config devices[6];
+	struct child_device_config devices[0];
 	/* may be another device block here on some platforms */
 } __attribute__((packed));