[PATCH] libata: convert ATAPI_ENABLE_DMADIR to module parameter

Convert the ATAPI_ENABLE_DMADIR compile time option needed
by some SATA-PATA bridge to runtime module parameter.

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>