fastboot: copy AVB footer from init_boot.img to end of partition

Similar to GKI boot.img, init_boot.img is released as a specific size
and should be able to be flashed into partitions that have different
sizes. So the AVB footer is moved from the end of the init_boot.img to
the end of the partition in the case that the partition is larger than
the image.

Bug: 203698939
Test: m
Change-Id: Ib5a63a7bf1b4be4eba4941972750f12e3edb3a17
diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index 32a22bb..ab429df 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -1076,7 +1076,8 @@
 {
     sparse_file** s;
 
-    if (partition == "boot" || partition == "boot_a" || partition == "boot_b") {
+    if (partition == "boot" || partition == "boot_a" || partition == "boot_b" ||
+        partition == "init_boot" || partition == "init_boot_a" || partition == "init_boot_b") {
         copy_boot_avb_footer(partition, buf);
     }