[SCSI] fusion - mptctl - backplane istwi fix

Moving the toolbox call from mptbase.c, over to
mptctl.c, and using the mptctl infastructure to issue
the call.  The existing code is hanging on certain HP platforms
when this ioctl is issued, and this patch fix's that.

Signed-off-by: Eric Moore <Eric.Moore@lsil.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>