Update UKI-specific scripts for arm64-compatibility.

reset_uki_cmdline.sh: Check for arch -> update naming to shim/grub {arch}.efi. For ARM64, there is no vmlinux B so added a check to exit if no vmlinux detected in ESP to continue and not fail.

set_uki_boot.sh: Check for arch -> update naming to shim/grub {arch}.efi.

BUG=none
TEST=presubmit, local tests
RELEASE_NOTE=none

Change-Id: I0d45a5ba63e226dc4d7354d6796867831a5700a2
Reviewed-on: https://cos-review.googlesource.com/c/third_party/platform/crosutils/+/181547
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
(cherry picked from commit eed6edbc36e26ec284829e59d98ab79a9c772c63)
Reviewed-on: https://cos-review.googlesource.com/c/third_party/platform/crosutils/+/212370
Tested-by: Dom Huh <domhuh@google.com>