drm/i915: Remove gen specific checks in MMIO

Now that MMIO has been split up into gen specific functions it is
obvious when HAS_FPGA_DBG_UNCLAIMED, HAS_FORCE_WAKE are needed. As such,
we can remove this extraneous condition.

As a result of this, as well as previously existing function pointers
for forcewake, we no longer need the has_force_wake member in the device
specific data structure.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>