[PATCH] sata_sil: implement R_ERR on DMA activate FIS errata fix

Silicon Image has disclosed a new sil3114/3152 errata and workaround
which causes the controller to return R_ERR on DMA activate FIS if the
FIS is received while the next PRD is being fetched.  This patch
implements the workaround.

This errata results in lock up and doesn't trigger if m15w workaround
is in effect.  We stopped applying m15w to 3512 and 3114 in 2.6.14-rc1
which makes 3512/3114 lock up with some drives on all kernel versions
since 2.6.14-rc1 upto now (2.6.16-rc4).  This patch should fix the
regression.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>