xfs: rename btree helpers that depends on the block number representation

xfs: rename btree helpers that depends on the block number representation

Source kernel commit: 5ef819c34f954fccfc42f79b9b0bea9b40cef9a1

All these helpers hardcode fsblocks or agblocks and not just the pointer
size.  Rename them so that the names are still fitting when we add the
long format in-memory blocks and adjust the checks when calling them to
check the btree types and not just pointer length.

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