tpm: move TPM space code out of tpm_transmit()

Prepare and commit TPM space before and after calling tpm_transmit()
instead of doing that inside tpm_transmit(). After this change we can
remove TPM_TRANSMIT_NESTED flag from tpm2_prepare_space() and
tpm2_commit_space() and replace it with TPM_TRANSMIT_UNLOCKED.

Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Tested-by: Alexander Steffen <Alexander.Steffen@infineon.com>