tpm: merge duplicate transmit_cmd() functions

Merged transmit_cmd() functions in tpm-interface.c and tpm-sysfs.c.
Added "tpm_" prefix for consistency sake. Changed cmd parameter as
opaque. This enables to use separate command structures for TPM1
and TPM2 commands in future. Loose coupling works fine here.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reviewed-by: Jasob Gunthorpe <jason.gunthorpe@obsidianresearch.com>
Reviewed-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Peter Huewe <peterhuewe@gmx.de>
Tested-by: Scot Doyle <lkml14@scotdoyle.com>
Tested-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>