vboot: unmarry LoadKernel from VBSD

Create a function-local copy of VbSharedDataKernelCall rather
than using the memory built-in to VBSD.  Stop making any
reference to vboot1 VBSD from LoadKernel.

BUG=b:124141368, chromium:1038260
TEST=make clean && make runtests
BRANCH=none

Change-Id: I5dabfb33a0eb05c1f40509dcf00a4c5751af1ef5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2053182
Tested-by: Joel Kitching <kitching@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
Reviewed-by: Joel Kitching <kitching@chromium.org>