sys-boot/shim: update to 15.4

Update RH EFI shim to version 15.4.

New ldscript file causes internal error in gold linker so force-use
bfd one.

BUG=b/186856815
TEST=presubmit
RELEASE_NOTE=Updated UEFI shim to 15.4.

Change-Id: I05e96be88cd623576e0b4d18369724630c45ae14
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/27580
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Reviewed-by: Roy Yang <royyang@google.com>
9 files changed