Oldland: don't zero extend sub-word loads.

ldr8/ldr16 zero extend by default so avoid a lsl+lsr pair.  This isn't
yet optimal yet - we can end up with:

	ldr8	$r0, [$r2, 0]
	mov	$r0, $r0

This is better than before - a lsl+lsr has been replaced with a mov, but
is still not optimal.  Ideally we'd eliminate that mov.