Add another command characteristic flag for commands that are queued

Add another command characteristic flag for commands that are queued
on physical devices as oposed to just in the XPT.  This is used to
mark XPT_SCSI_IO, XPT_RESET_DEV, XPT_ENG_EXEC, XPT_TARGET_IO, and
XPT_CONT_TARGET_IO function codes.

Change tag_id and init_id to be u_int from u_int8_t.  Some topologies
supported by CAM support much larger ID and tag ID address spaces
than parallel SCSI.

Kill some unused fields in the IMMED_NOTIFY ccb type.