[PATCH] libata irq-pio: add read/write multiple support

   - add is_multi_taskfile() to ata.h
   - initialize ata_device->multi_count with device identify data
   - use ata_pio_sectors() to support r/w multiple commands

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
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Signed-off-by: Jeff Garzik <jgarzik@pobox.com>