drm/msm/dp: stop event kernel thread when DP unbind

Current DP driver implementation, event thread is kept running
after DP display is unbind. This patch fix this problem by disabling
DP irq and stop event thread to exit gracefully at dp_display_unbind().

Changes in v2:
-- start event thread at dp_display_bind()

Changes in v3:
-- disable all HDP interrupts at unbind
-- replace dp_hpd_event_setup() with dp_hpd_event_thread_start()
-- replace dp_hpd_event_stop() with dp_hpd_event_thread_stop()
-- move init_waitqueue_head(&dp->event_q) to probe()
-- move spin_lock_init(&dp->event_lock) to probe()

Changes in v4:
-- relocate both dp_display_bind() and dp_display_unbind() to bottom of file

Changes in v5:
-- cancel relocation of both dp_display_bind() and dp_display_unbind()

Changes in v6:
-- move empty event q to dp_event_thread_start()

Changes in v7:
-- call ktheread_stop() directly instead of dp_hpd_event_thread_stop() function

Changes in v8:
-- return error immediately if audio registration failed.

Changes in v9:
-- return error immediately if event thread create failed.

Changes in v10:
-- delete extra  DRM_ERROR("failed to create DP event thread\n");

Fixes: 8ede2ecc ("drm/msm/dp: Add DP compliance tests on Snapdragon Chipsets")
Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reported-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/482399/
Link: https://lore.kernel.org/r/1650318988-17580-1-git-send-email-quic_khsieh@quicinc.com


[DB: fixed Fixes tag]
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>