drm/i915: Explicitly convert some macros to boolean values

Some IS_ and HAS_ macros can return any non-zero value for true.

One potential problem with that is that someone could assign
them to integers and be surprised with the result. Therefore it
is probably safer to do the conversion to 0/1 in the macros
themselves.

Luckily this does not seem to have an effect on code size.

Only one call site was getting bit by this and a patch for
that has been sent as "drm/i915/guc: Protect against HAS_GUC_*
returning true values other than one".

v2: Added some extra braces as suggested by checkpatch.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1467643823-9798-1-git-send-email-tvrtko.ursulin@linux.intel.com