PCI/DOE: Relax restrictions on request and response size

An upcoming user of DOE is CMA (Component Measurement and Authentication,
PCIe r6.0 sec 6.31).

It builds on SPDM (Security Protocol and Data Model):
https://www.dmtf.org/dsp/DSP0274

SPDM message sizes are not always a multiple of dwords.  To transport
them over DOE without using bounce buffers, allow sending requests and
receiving responses whose final dword is only partially populated.

To be clear, PCIe r6.0 sec 6.30.1 specifies the Data Object Header 2
"Length" in dwords and pci_doe_send_req() and pci_doe_recv_resp()
read/write dwords.  So from a spec point of view, DOE is still specified
in dwords and allowing non-dword request/response buffers is merely for
the convenience of callers.

Tested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Ming Li <ming4.li@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/151b1a6a1794afb65d941287ecbc032c5b8004b9.1678543498.git.lukas@wunner.de
Signed-off-by: Dan Williams <dan.j.williams@intel.com>