CuPy support

#### Is your feature request related to a problem? Please describe.
I wonder if it is possible to use [cupy-xarray](https://github.com/xarray-contrib/cupy-xarray) to accelerate on demand post proccessing of large geospatial datasets and visualization via (datashader)

#### Describe the solution you'd like

In an ideal world just a backend detector that would allow for the same functionality of hvplot for CuPy as it would for a NumPy or Dask backed Xarray DataArray.

#### Describe alternatives you've considered
Right now I use the Dask backed Xarray DataArrays and `datashade=True` in `hvplot.image` which is almost fast enough for some of my more advanced applications.