[WHY]
To add support for HPD interrupt handling from DMUB.
HPD interrupt could be triggered from outbox1 from DMUB

[HOW]
1) Use queue_work to handle hpd task from outbox1

2) Add handle_hpd_irq_helper to share interrupt handling code
between legacy and DMUB HPD from outbox1

3) Added DMUB HPD handling in dmub_srv_stat_get_notification().
HPD handling callback function and wake up the DMUB thread.
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Jude Shih <shenshih@amd.com>
Tested-by: Daniel Wheeler <Daniel.Wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>