dax: Check the end of the block-device capacity with dax_direct_access()

dax: Check the end of the block-device capacity with dax_direct_access()

The checks in __bdev_dax_supported() helped mitigate a potential data
corruption bug in the pmem driver's handling of section alignment
padding. Strengthen the checks, including checking the end of the range,
to validate the dev_pagemap, Xarray entries, and sector-to-pfn
translation established for pmem namespaces.

Acked-by: Jan Kara <[email protected]>
Cc: "Darrick J. Wong" <[email protected]>
Signed-off-by: Dan Williams <[email protected]>