Update bootloader, u-boot tools to builds 7845945 am: ae1b2f349c am: b312be3a07

Original change: https://android-review.googlesource.com/c/device/google/cuttlefish_prebuilts/+/1868054

Change-Id: I46195f4fb5e55e1d0bda53326d43c8d1ef83b59e