build: make libblkid usage optional

build: make libblkid usage optional

Because not all platforms have up-to-date blkid with required
functions, allow at least partial functionality by adding
--enable-blkid=yes/no optional configure argument.

When blkid is disabled, signature detection and device geometry
detection doesn't work.

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