drm/i915: Don't request GMBUS to generate irqs when called while irqs are off

We will need to do some i2c poking from the encoder->shutdown() hook.
Currently that gets called after irqs have been turned off. We still
poll the gmbus status bits even if the interrupt never arrives so
things will work just fine. But seems like asking gmbus to generate
interrupts we will never see is a bit pointless, so don't.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211029191802.18448-1-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>