Add unmapped I/O and larger I/O support to the sa(4) driver.

We now pay attention to the maxio field in the XPT_PATH_INQ CCB,
and if it is set, propagate it up to physio via the si_iosize_max
field in the cdev structure.

We also now pay attention to the PIM_UNMAPPED capability bit in the
XPT_PATH_INQ CCB, and set the new SI_UNMAPPED cdev flag when the
underlying SIM supports unmapped I/O.

scsi_sa.c:	Add unmapped I/O support and propagate the SIM's
		maximum I/O size up.

		Adjust scsi_tape_read_write() in the same way that
		scsi_read_write() was changed to support unmapped
		I/O.  We overload the readop parameter with bits
		that tell us whether it's an unmapped I/O, and we
		need to set the CAM_DATA_BIO CCB flag.  This change
		should be backwards compatible in source and
		binary forms.

MFC after:	1 week
Sponsored by:	Spectra Logic
When we need to build using the in-tree make,
switch at the earliest opportunity.
In the case of fmake vs bmake, this helps ensure correct load handling.

Reviewed by: obrien