tpm: own sysfs group for pcrs for TPM2 devices

Modified driver to create sysfs group "pcr" for PCRs. For each
PCR this group contains a separate attribute named with the index
number of the PCR. PCR is presented as a hex string.

Attributes are created dynamically so that it is easy to later on
use TPM_PT_PCR_COUNT TPM property read the number of PCRs available
instead of only supporting the minimum PCRs required by the TPM2
standard.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>