drivers/char/tpm: Add new device driver to support IBM vTPM

This patch adds a new device driver to support IBM virtual TPM
(vTPM) for PPC64.  IBM vTPM is supported through the adjunct
partition with firmware release 740 or higher.  With vTPM
support, each lpar is able to have its own vTPM without the
physical TPM hardware.

This driver provides TPM functionalities by communicating with
the vTPM adjunct partition through Hypervisor calls (Hcalls)
and Command/Response Queue (CRQ) commands.

Signed-off-by: Ashley Lai <adlai@us.ibm.com>
Signed-off-by: Kent Yoder <key@linux.vnet.ibm.com>