tpm: use u32 instead of int for PCR index

The TPM specs defines PCR index as a positive number, and there is
no reason to use a signed number. It is also a possible security
issue as currently no functions check for a negative index,
which may become a large number when converted to u32.

Adjust the API to use u32 instead of int in all PCR related
functions.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>