Enabled HALF for fill() and zero() methods. Moved them into THTensorFill (#17536)
Summary:
For some additional context on this change, please, see this [PR](https://github.com/pytorch/pytorch/pull/17376)
As a part of work on Bool Tensor, we will need to add support for a bool type to _fill() and _zero() methods that are currently located in THTensorMath. As we don't need anything else and those methods are not really math related - we are moving them out into separate THTensorFill for simplicity.
Change:
-moved _fill() and _zero() from THTensorMath.h to THTensorFill
-enabled _fill() and _zero() for HALF type.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17536
Differential Revision: D14242130
Pulled By: izdeby
fbshipit-source-id: 1d8bd806f0f5510723b9299d360b70cc4ab96afb
