disp: msm: sde: fix potential race condition

Move the hist irq handling out of callback function, i.e., the hw
interrupt irq_lock context, to avoid dead lock between crtc spin_lock
and irq_lock. This change also extends crtc spin_lock coverage in
_sde_cp_crtc_enable_hist_irq to prevent null pointer dereference on
event node, which can be deleted during crtc event de-registration.

Change-Id: Iadaed54ab93c4c4abe065a8762d2addccb0c65c6
Signed-off-by: Ping Li <pingli@codeaurora.org>

msm/sde/sde_crtc.h

@@ -290,6 +290,7 @@ struct sde_crtc_misr_info {
  * @ltm_buffer_lock : muttx to protect ltm_buffers allcation and free
  * @ltm_lock        : Spinlock to protect ltm buffer_cnt, hist_en and ltm lists
  * @needs_hw_reset  : Initiate a hw ctl reset
+ * @hist_irq_idx    : hist interrupt irq idx
  * @src_bpp         : source bpp used to calculate compression ratio
  * @target_bpp      : target bpp used to calculate compression ratio
  * @static_cache_read_work: delayed worker to transition cache state to read
@@ -383,6 +384,7 @@ struct sde_crtc {
 	struct mutex ltm_buffer_lock;
 	spinlock_t ltm_lock;
 	bool needs_hw_reset;
+	int hist_irq_idx;
 
 	int src_bpp;
 	int target_bpp;