[PATCH] sil: apply M15W quirk selectively (take 2)

 As SII reports that only original 3112's are affected by M15W quirk,
This patch adds SIL_FLAG_MOD15WRITE to selectively apply M15W quirk
depending on chipsets.  As of yet, we don't know exactly which PCI IDs
are for original 3112, so M15W quirk is applied to all except for 3512
and 3124.  Once more info is avaliable, we can change some of these
sil_3112_m15w's to sil_3112.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>