drm/xe/display: use xe && 0 to avoid warnings about unused variables

Avoid warnings about unused variables when the IS_LP(), IS_GEN9_LP(),
and IS_GEN9_BC() macros are the only users of a variable. This is not
currently the case, but prepare for future changes.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/2a9960df4d9f6423a2cc6a29a7a7b0c1420690c7.1725012870.git.jani.nikula@intel.com

Author: jnikula

drivers/gpu/drm/xe/compat-i915-headers/i915_drv.h

@@ -75,9 +75,9 @@ static inline struct drm_i915_private *to_i915(const struct drm_device *dev)
 
 #define IS_MOBILE(xe) (xe && 0)
 
-#define IS_LP(xe) (0)
-#define IS_GEN9_LP(xe) (0)
-#define IS_GEN9_BC(xe) (0)
+#define IS_LP(xe) ((xe) && 0)
+#define IS_GEN9_LP(xe) ((xe) && 0)
+#define IS_GEN9_BC(xe) ((xe) && 0)
 
 #define IS_TIGERLAKE_UY(xe) (xe && 0)
 #define IS_COMETLAKE_ULX(xe) (xe && 0)