MFC r343814 (by imp): Add quirk for Sansisk X400 drives

MFC r343814 (by imp): Add quirk for Sansisk X400 drives

Certain versions of Sandisk x400 firmware can hang under extremely
heavly load of large I/Os for prolonged periods of time. Newer /
current versions work fine, and should be used where possible. Where
not possible, this quirk ensures that I/O requests are limited to 128k
to avoids the bug, even under extreme load. Since MAXPHYS is 128k,
only users with custom kernels are at risk on the older firmware.
Once all known users of the older firmware have upgraded, this quirk
will be removed.