xfs: hoist recovered extent-free intent checks out of xfs_efi_item_recover

When we recover a extent-free intent from the log, we need to validate
its contents before we try to replay them.  Hoist the checking code into
a separate function in preparation to refactor this code to use
validation helpers.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>