tcgbios: Use The proper sha function for each PCR bank

Instead of just using sha256 for all PCR banks (and truncating
the value or zero-padding it) use the proper hash function for
each one of the banks. For unimplemented hashes, fill the buffer
with 0xff.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>