Tell CAM that SPI disconnect works, which in turn will let it use tags.

This fixes the low "max device openings" count that has lead to poor
performance in FreeBSD 7.0 and 7.1.

Extra thanks goes to Mike Tancsa at Sentex for providing a debug system for
this.

sys/dev/arcmsr/arcmsr.c

@@ -2150,7 +2150,8 @@ static void arcmsr_action(struct cam_sim * psim, union ccb * pccb)
 				spi->sync_offset=32;
 				spi->bus_width=MSG_EXT_WDTR_BUS_16_BIT;
 				scsi->flags = CTS_SCSI_FLAGS_TAG_ENB;
-				spi->valid = CTS_SPI_VALID_SYNC_RATE
+				spi->valid = CTS_SPI_VALID_DISC
+					| CTS_SPI_VALID_SYNC_RATE
 					| CTS_SPI_VALID_SYNC_OFFSET
 					| CTS_SPI_VALID_BUS_WIDTH;
 				scsi->valid = CTS_SCSI_VALID_TQ;