vboot/vboot_kernel: rewrite kernel version checking code
vboot/vboot_kernel: rewrite kernel version checking code

This CL is part of a series to merge vboot1 and vboot2.0
kernel verification code; see b/181739551.

BUG=b:181739551
TEST=make clean && make runtests
BRANCH=none

Signed-off-by: Joel Kitching <c2feea8c1334a0d339e816ae4c7c9ecfa9b30a91@google.com>
Change-Id: I18790fefe7c4bf2126978c7a9bf1d412dfc8ac78
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2785809
Tested-by: Joel Kitching <c2feea8c1334a0d339e816ae4c7c9ecfa9b30a91@chromium.org>
Reviewed-by: Julius Werner <4d12f06cff3725783b352157673a720bc67c4afe@chromium.org>
Commit-Queue: Joel Kitching <c2feea8c1334a0d339e816ae4c7c9ecfa9b30a91@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot