tpm_tis: move buffers from localities into common location

One read buffer and one write buffer is sufficient for all localities.
The localities cannot all be active at the same time, and only the active
locality can use the r/w buffers. Inactive localities will require the
COMMAND_READY flag to be set on the STS register to move to the READY
state, which then enables access to using the buffer for writing of a
command, while all other localities are inactive.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>