util/grub-protect: Support NV index mode

util/grub-protect: Support NV index mode

This commit implements the missing NV index mode support in grub-protect.
NV index mode stores the sealed key in the TPM non-volatile memory (NVRAM)
instead of a file. There are two supported types of TPM handles.

1. Persistent handle (0x81000000~0x81FFFFFF)
   Only the raw format is supported due to the limitation of persistent
   handles. This grub-protect command seals the key into the
   persistent handle 0x81000000.

  # grub-protect \
      --protector=tpm2 \
      --action=add \
      --tpm2-bank=sha256 \
      --tpm2-pcrs=7,11 \
      --tpm2-keyfile=luks-key \
      --tpm2-nvindex=0x81000000

2. NV index handle (0x1000000~0x1FFFFFF)
   Both TPM 2.0 Key File format and the raw format are supported by NV
   index handles. Here is the grub-protect command to seal the key in
   TPM 2.0 Key File format into the NV index handle 0x1000000.

  # grub-protect \
      --protector=tpm2 \
      --action=add \
      --tpm2key \
      --tpm2-bank=sha256 \
      --tpm2-pcrs=7,11 \
      --tpm2-keyfile=luks-key \
      --tpm2-nvindex=0x1000000

Besides the "add" action, the corresponding "remove" action is also
introduced. To remove the data from a persistent or NV index handle,
just use "--tpm2-nvindex=HANDLE" combining with "--tpm2-evict". This
sample command removes the data from the NV index handle 0x1000000.

  # grub-protect \
      --protector=tpm2 \
      --action=remove \
      --tpm2-evict \
      --tpm2-nvindex=0x1000000

Also set and check the boolean variables with true/false instead of 1/0.

Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>