xfs: hide xfs_icache_free_eofblocks

Change the one remaining caller of xfs_icache_free_eofblocks to use our
new combined blockgc scan function instead, since we will soon be
combining the two scans.  This introduces a slight behavior change,
since the XFS_IOC_FREE_EOFBLOCKS now clears out speculative CoW
reservations in addition to post-eof blocks.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>