PcrSlot wont compile if TPM2_PCR_SELECT_MAX != 4

[Superhepper]

If a platform has defined TPM2_PCR_SELECT_MAX != 4. The PcrSlot enum will cause compilation failure. It expects the buffer to hold the bit field octets to be four bytes. It needs to support lower values of TPM2_PCR_SELECT_MAX as well.

And should produce an error if the selected slot cannot fit inside the octets specified by TPM2_PCR_SELECT_MAX.