drm/i915: Use the correct IRQ during resume

The code in xcs_resume() probably didn't work as intended. It uses
struct drm_device.irq, which is allocated to 0, but never initialized
by i915 to the device's interrupt number.

Change all calls to synchronize_hardirq() to intel_synchronize_irq(),
which uses the correct interrupt. _hardirq() functions are not needed
in this context.

v5:
	* go back to _hardirq() after PCI probe reported wrong
	  context; add rsp comment
v4:
	* switch everything to intel_synchronize_irq() (Daniel)
v3:
	* also use intel_synchronize_hardirq() at another callsite
v2:
	* wrap irq code in intel_synchronize_hardirq() (Ville)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 536f77b1 ("drm/i915/gt: Call stop_ring() from ring resume, again")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210701173618.10718-2-tzimmermann@suse.de