drm/i915: Make IS_GENx macros work on a mask

If instead of numerical comparison me make these test a
bitmask, we enable the compiler to optimize all instances
of IS_GENx || IS_GENy.

v2: Make bit zero of gen mask mean gen 1.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index b55fef3..81856f1 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1073,6 +1073,9 @@
 	memcpy(device_info, info, sizeof(dev_priv->info));
 	device_info->device_id = dev->pdev->device;
 
+	BUG_ON(device_info->gen > sizeof(device_info->gen_mask) * BITS_PER_BYTE);
+	device_info->gen_mask = BIT(device_info->gen - 1);
+
 	spin_lock_init(&dev_priv->irq_lock);
 	spin_lock_init(&dev_priv->gpu_error.lock);
 	mutex_init(&dev_priv->backlight_lock);