drm/msm/dpu: drop dpu_encoder_phys_ops.atomic_mode_set

The atomic_mode_set() callback only sets the phys_enc's IRQ data. As the
INTF and WB are statically allocated to each encoder/phys_enc, drop the
atomic_mode_set callback and set the IRQs during encoder init.

For the CMD panel usecase some of IRQ indexes depend on the selected
resources. Move setting them to the irq_enable() callback.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Tested-by: Abhinav Kumar <quic_abhinavk@quicinc.com> # sc7280
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/577529/
Link: https://lore.kernel.org/r/20240208-fd_remove_phys_ops_atomic_mode_set-v4-3-caf5dcd125c0@linaro.org