ide: add ide_execute_pkt_cmd() helper

Add ide_execute_pkt_cmd() helper for executing PACKET command,
then convert ATAPI device drivers to use it.

As a nice side-effect this fixes ide-{floppy,tape,scsi} w.r.t.
ide_lock taking (ide-cd was OK).

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/ide-tape.c b/drivers/ide/ide-tape.c
index dc88431..71d07d7 100644
--- a/drivers/ide/ide-tape.c
+++ b/drivers/ide/ide-tape.c
@@ -1056,9 +1056,7 @@
 				    IDETAPE_WAIT_CMD, NULL);
 		return ide_started;
 	} else {
-		hwif->OUTBSYNC(drive, WIN_PACKETCMD,
-			       hwif->io_ports.command_addr);
-		ndelay(400);
+		ide_execute_pkt_cmd(drive);
 		return idetape_transfer_pc(drive);
 	}
 }