drm/i915: Remove unused HAS_FWTABLE macro

It has been unused since commit ccb2acea

 ("drm/i915: use vfuncs for
reg_read/write_fw_domains").

Signed-off-by: Pascal Terjan <pterjan@google.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200510212521.128869-1-pterjan@google.com