xfsprogs: only install *format.h headers in install-qa

xfsprogs: only install *format.h headers in install-qa

Now that we've properly split up the headers we don't need to install all
the libxfs-internal headers for xfstests.  Just install the three headers
defining the on-disk format and xfs_arch.h which is required to compile
them instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>