DAX error handling for 4.7

- Until now, dax has been disabled if media errors were found on
  any device. This enables the use of DAX in the presence of these
  errors by making all sector-aligned zeroing go through the driver.
- The driver (already) has the ability to clear errors on writes that
  are sent through the block layer using 'DSMs' defined in ACPI 6.1.

Other misc changes:

- When mounting DAX filesystems, check to make sure the partition
  is page aligned. This is a requirement for DAX, and previously, we
  allowed such unaligned mounts to succeed, but subsequent reads/writes
  would fail.

- Misc/cleanup fixes from Jan that remove unused code from DAX related to
  zeroing, writeback, and some size checks.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iQIcBAABAgAGBQJXQ4GKAAoJEHr6Yb6juE3/zowP/iclIhgXXXMQJRUHJlePMXC8
15sGZ32JS1ak9g7vrsmNVEDNynfNtiMYdBxtUyRuj6xqgwdZvFk3F55KOCPtaeA1
+yADkgeRkTAcwzmHw9WQVEzBCqyzSisdrwtEfH817qdq9FJdH66x2Kos6i+HeAVr
5Q/e4gs7lKrjf384/QBl+wxNZOndJaQAPd2VRHQqx2A9F33v0ljdwRaUG1r4fjK2
dtmhcZCqdQyuAGXW3piTnZc5ZFc3DPqO4FkEfqkEK3lFOflK0fd8wMsAZRp/Jd0j
GJsgnVSWSqG0Dz476djlG0w8t2p5Jv1g9cKChV+ZZEdFLKWHCOUFqXNj8uI8I4k5
cOEKCHyJ3IwfSHhNQqktEWrQN4T8ZXhWtuc9GuV4UZYuqJqHci6EdR/YsWsJjV+L
lm/qvK4ipDS1pivxOy8KX/iN0z7Io8J9GXpStDx3g8iWjLlh4YYlbJLWeeRepo/z
aPlV/QAKcHiGY6jzLExrZIyCWkzwo6O+0p1Kxerv9/7K/32HWbOodZ+tC8eD+N25
pV69nCGf+u50T2TtIx1+iann4NC1r7zg5yqnT9AgpyZpiwR5joCDzI5sXW+D0rcS
vPtfM84Ccdeq/e6mvfIpZgR0/npQapKnrmUest0J7P2BFPHiFPji1KzZ7M+1aFOo
9R6JdrAj0Sc+FBa+cGzH
=v6Of
-----END PGP SIGNATURE-----