vboot: convert LoadKernel and TryLoadKernel to vboot2-style errors

Convert LoadKernel and TryLoadKernel to use vboot2-style error
codes.  Error codes are renamed as follows:

  VBERROR_NO_KERNEL_FOUND
  --> VB2_ERROR_LK_NO_KERNEL_FOUND

  VBERROR_INVALID_KERNEL_FOUND
  --> VB2_ERROR_LK_INVALID_KERNEL_FOUND

  VBERROR_NO_DISK_FOUND
  --> VB2_ERROR_LK_NO_DISK_FOUND

Remove these error codes:

  VBERROR_LOAD_KERNEL_RECOVERY
    Remove VBSD_BOOT_DEV_SWITCH_ON check in vb2_developer_ui
    to align vboot_ui and vboot_ui_menu functionality.

  VBERROR_LOAD_KERNEL
    Unused.

BUG=b:124141368, chromium:988410
TEST=make clean && make runtests
BRANCH=none

Change-Id: I90389c6629cc6055c4a4acbbbdd358bb79b63bf7
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1728297
Tested-by: Joel Kitching <kitching@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
Reviewed-by: Joel Kitching <kitching@chromium.org>
10 files changed