Fix issues where int64 crops could not be passed to batch_to_space. (#13862)

* Fix issues where int64 crops could not be passed to batch_to_space.

This fix tries to address the issue where int64 `crops` could
not be passed to `batch_to_space` even though both int32 and
int64 are specified as supported in the docs (tf.batch_to_space.__doc__)

The reason is that BatchToSpace kernel puts a constraint of int32 to crops
data types.

This fix removed the constraint so that int64 `crops` could be supported.

NOTE: Just removing the constraint should work and it is not necessary
to add specification to the kernel class template, as `SubtleMustCopyFlat`
called in the class already correctly handled both int32 and int64 cases.
Besides, other data types (e.g., float or double) will not be passed to the
kernel as they are guarded by the specification in `array_ops.cc`.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Also remove int64/int32 type constraints for SpaceToBatch kernels

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Add test cases for int64 crops of batch_to_space and space_to_batch

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Fix test failures.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>