drm/i915: use in_interrupt() not in_irq() to check context

The kernel in_irq() function tests for hard-IRQ context only, so if a
system is run with the kernel 'threadirqs' option selected, the test in
intel_check_page_flip() generates lots of warnings, because then it gets
called in soft-IRQ context.

We can instead use in_interrupt() which allows for either type of
interrupt, while still detecting and complaining about misuse of the
page flip code if it is ever called from non-interrupt context.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89321
Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -9716,7 +9716,7 @@ void intel_check_page_flip(struct drm_device *dev, int pipe)
 	struct drm_crtc *crtc = dev_priv->pipe_to_crtc_mapping[pipe];
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
 
-	WARN_ON(!in_irq());
+	WARN_ON(!in_interrupt());
 
 	if (crtc == NULL)
 		return;