sd-boot: put hashed kernel command line in a PCR of the TPM

sd-boot: put hashed kernel command line in a PCR of the TPM

The UEFI BIOS already hashes the contents of the loaded image, so the
initrd and the command line of the binary are recorded.

Because manually added LoadOptions are not taken into account, these
should be recorded also.

This patch logs and extends a TPM PCR register with the LoadOptions.

This feature can be enabled with configure --enable-tpm

The PCR register index can be specified with
configure --with-tpm-pcrindex=<NUM>