drm/msm/dpu: allow just single IRQ callback

drm/msm/dpu: allow just single IRQ callback

DPU interrupts code allows multiple callbacks per interrut. In reality
none of the interrupts is shared between blocks (and will probably never
be). Drop support for registering multiple callbacks per interrupt to
simplify interrupt handling code.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/474701/
Link: https://lore.kernel.org/r/20220217043148.480898-4-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>