drm/i915: Check for duplicated power well IDs

Check that all the power well IDs are unique on the given platform.

v2:
- Fix using BIT_ULL() instead of BIT() for 64 bit mask.
v3:
- Move the check to a separate function. (Ville)

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170711204236.5618-4-imre.deak@intel.com


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>