If dpctl is not found then Numba crashed

[diptorupd]

Numba should not crash if dpctl is not present. I encountered this when I tried to import numba without first installing dpctl. This should be fixed before beta 10.

(numba-dpctl-devel) diptorup@ansatnuc06:/localdisk/work/diptorup/devel/numba$ python
Python 3.7.8 | packaged by conda-forge | (default, Jul 31 2020, 02:25:08)
[GCC 7.5.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import numba
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/localdisk/work/diptorup/devel/numba/numba/__init__.py", line 213, in <module>
    import numba.typed
  File "/localdisk/work/diptorup/devel/numba/numba/typed/__init__.py", line 1, in <module>
    from .typeddict import Dict
  File "/localdisk/work/diptorup/devel/numba/numba/typed/typeddict.py", line 22, in <module>
    @njit
  File "/localdisk/work/diptorup/devel/numba/numba/core/decorators.py", line 271, in njit
    return jit(*args, **kws)
  File "/localdisk/work/diptorup/devel/numba/numba/core/decorators.py", line 179, in jit
    return wrapper(pyfunc)
  File "/localdisk/work/diptorup/devel/numba/numba/core/decorators.py", line 232, in __wrapper
    from numba.dppl.target_dispatcher import TargetDispatcher
  File "/localdisk/work/diptorup/devel/numba/numba/dppl/__init__.py", line 513, in <module>
    raise ImportError("Importing dppl failed")
ImportError: Importing dppl failed