Imports Chris Liu Comstar SCSI passthrough patch

From the 2008 mail announcing this never integrated
comstar passthrough LU provider.

I have developed a prototype LU provider working
with COMSTAR. It passes through all incoming commands
to registered devices and all data to initiator. Thus, it
can transparently export local disks/tapes/CD(DVD)-R(RW)
to remote host through COMSTAR framework. I name it spd
(SCSI passthrough device).

Go to usr/src/uts/intel/stmf_spd/ or usr/src/uts/sparc/stmf_spd/,
make the binaries - stmf_spd.

Put binaries (32bit and 64bit) in /kernel/drv/ and /kernel/drv/amd64
respectively, copy stmf_spd.conf from workspace to /kernel/drv, run:
add_drv stmf_spd

Build the managerment utility spdadm from workspace usr/src/cmd/spdadm.
Run it to register/deregister/list LUs.

Currently, I open devices as blocking devices only, so CD/DVD disc must
be loaded prior to register it as LU. This will be handled better later.

It is still a prototype and will NOT ensure your data safety.