bootsignature: includes dt image size for signed boot image

BootSignature truncates the bootimage since dt image size wasn't
considered while calculating the signable bootimage size and thus
target fails to boot. This patch includes the device tree size in
the boot image and prevents it from truncating it and makes the
target boot fine.

[Jarl-Penguin]: Adapted for Android 12

Issue-id: YAM-27
Change-Id: Ieaa396159130875768231602cd58eb865d222872

verity/BootSignature.java

@@ -239,6 +239,9 @@ public static int getSignableImageSize(byte[] data) throws Exception {
                         "Invalid image header: invalid header length");
             }
         }
+        if (headerVersion > 4) {
+            length = length + ((headerVersion + pageSize - 1) / pageSize) * pageSize;
+        }
 
         length = ((length + pageSize - 1) / pageSize) * pageSize;