checkpatch: Detect newlines in error_report and other error functions

We don't want newlines embedded in error messages. This seems to be a common
problem with new code so let's try to catch it with checkpatch.

This will not catch cases where newlines are inserted into the middle of an
existing multi-line statement. But those cases should be rare.

Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>
Message-Id: <1449858642-24267-1-git-send-email-jjherne@linux.vnet.ibm.com>
[Rephrased "Error function text" to "Error messages", dropped
error_vprintf, error_printf, error_printf from $qemu_error_funcs,
because they may legitimately print newlines]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
