tpm: add ptr to the tpm_space struct to file_priv

Add a ptr to struct tpm_space to the file_priv and consolidate
of the write operations for the two interfaces.

Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
Tested-by: Philip Tricca <philip.b.tricca@intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off--by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>