soc/intel/common: refactor locate_vbt and vbt_get

Instead of having all callers provide a region_device just for the
purpose of reading vbt.bin, let locate_vbt handle its entire life cycle,
simplifying the VBT access API.

Change-Id: Ib85e55164e217050b67674d020d17b2edf5ad14d
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/21897
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/drivers/intel/fsp2_0/graphics.c

@@ -96,10 +96,7 @@ enum cb_err fsp_fill_lb_framebuffer(struct lb_framebuffer *framebuffer)
 
 uintptr_t fsp_load_vbt(void)
 {
-	struct region_device rdev;
-	void *vbt_data = NULL;
-
-	vbt_data = locate_vbt(&rdev);
+	void *vbt_data = locate_vbt();
 
 	if (vbt_data == NULL)
 		printk(BIOS_NOTICE, "Could not locate a VBT file in CBFS\n");