drm/i915/gvt: Fix emulated vbt size issue

The emulated vbt doesn't tell its size correctly. According to the
intel_vbt_defs.h, vbt_header.vbt_size should the size of VBT (VBT Header,
BDB Header and data blocks), and bdb_header.bdb_size should be the size
of BDB (BDB Header and data blocks).

This patch fixes the issue and lets vbt provided by GVT-g pass the guest
i915's sanity test.

v2: refine the commit message. (Zhenyu)
Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200305131600.29640-1-tina.zhang@intel.com

drivers/gpu/drm/i915/gvt/opregion.c

@@ -147,15 +147,14 @@ static void virt_vbt_generation(struct vbt *v)
 	/* there's features depending on version! */
 	v->header.version = 155;
 	v->header.header_size = sizeof(v->header);
-	v->header.vbt_size = sizeof(struct vbt) - sizeof(v->header);
+	v->header.vbt_size = sizeof(struct vbt);
 	v->header.bdb_offset = offsetof(struct vbt, bdb_header);
 
 	strcpy(&v->bdb_header.signature[0], "BIOS_DATA_BLOCK");
 	v->bdb_header.version = 186; /* child_dev_size = 33 */
 	v->bdb_header.header_size = sizeof(v->bdb_header);
 
-	v->bdb_header.bdb_size = sizeof(struct vbt) - sizeof(struct vbt_header)
-		- sizeof(struct bdb_header);
+	v->bdb_header.bdb_size = sizeof(struct vbt) - sizeof(struct vbt_header);
 
 	/* general features */
 	v->general_features_header.id = BDB_GENERAL_FEATURES;