configure: simplify the qemu cpu mapping

Use AS_CASE to properly map from the host cpu to the qemu cpu suffix;
this avoids doing multiple string replacements using sed, and it is
possible to use case-like syntax.
daemon: check xfs label lengths (RHBZ#1162966).

Similar to commit 52f9cd4882135910ea06e1e50ac6441d455c9ab1, but for xfs
filesystems.