x86: zboot: Set environment variables for image locations

At present it is not possible to tell from a script where the setup block
is, or where the image was loaded to. Add environment variables for this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/README b/README
index 6cb0567..5132b22 100644
--- a/README
+++ b/README
@@ -3425,6 +3425,10 @@
   mempos	- Index position of the last match found by the 'ms' command,
 		  in units of the size (.b, .w, .l) of the search
 
+  zbootbase	- (x86 only) Base address of the bzImage 'setup' block
+
+  zbootaddr	- (x86 only) Address of the loaded bzImage, typically
+		  BZIMAGE_LOAD_ADDR which is 0x100000
 
 The following image location variables contain the location of images
 used in booting. The "Image" column gives the role of the image and is