msm_fb: HDMI: Cleanup HPD software debouncing logic

Implement Hot Plug Detect (HPD) software debouncing by
disabling the HPD interrupt until we finish processing
a previous HPD interrupt.

CRs-Fixed: 412575
Change-Id: Ia2c83f3446d09fe5bf6c6a1c4e6a9eb54ff465d6
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>