drm/msm/dpu: simplify IRQ enabling/disabling

Merge dpu_core_irq_enable() into dpu_core_irq_register_callback() and
dpu_core_irq_disable() into dpu_core_irq_unregister_callback(), because
they are called in pairs. There is no need to have separate
enable/disable pair, we can enable hardware IRQ when first callback is
registered and when the last callback is unregistered.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Link: https://lore.kernel.org/r/20210516202910.2141079-7-dmitry.baryshkov@linaro.org


[fixup tracepoint compile warns]
Signed-off-by: Rob Clark <robdclark@chromium.org>