ABI: add sysfs description for tpm exports of PCR registers

Adds the ABI entries for the new

/sys/class/tpm/tpm<n>/pcr-<hash>/<m>

files which are added to export the PCR hash values on a one value per
file basis.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>