Create new EINTEGRITY error with message "Integrity check failed".

Create new EINTEGRITY error with message "Integrity check failed".

An integrity check such as a check-hash or a cross-correlation failed.
The integrity error falls between EINVAL that identifies errors in
parameters to a system call and EIO that identifies errors with the
underlying storage media. EINTEGRITY is typically raised by intermediate
kernel layers such as a filesystem or an in-kernel GEOM subsystem when
they detect inconsistencies. Uses include allowing the mount(8) command
to return a different exit value to automate the running of fsck(8)
during a system boot.

These changes make no use of the new error, they just add it. Later
commits will be made for the use of the new error number and it will
be added to additional manual pages as appropriate.

Reviewed by:    gnn, dim, brueffer, imp
Discussed with: kib, cem, emaste, ed, jilles
Differential Revision: https://reviews.freebsd.org/D18765