Support TPM2_PCR_Allocate command

[zhsh]

Our primary motivation for supporting the TPM2_PCR_Allocate command is that we would like to be able to pre-configure the TPM Simulator with a given list of PCR registers for unit tests.

By default, the TPM Simulator comes with a number of PCR banks (one per each supported algorithm), and each PCR bank has 24 registers. But some physical TPMs may come with PCR bank(s) that have zero registers (e.g. SHA1 bank with 0 registers, and SHA256 bank with 24 registers). If we want to have a TPM Simulator with a similar configuration of PCR registers, we need to modify the list of available registers somehow; and that's where TPM2_PCR_Allocate is going to be useful.

There are probably other use cases that need TPM2_PCR_Allocate too.