drm/bridge/sii8620: start MHL transmission after HDMI signal detection

The vendor code waits for infoframe to detect video mode set by source.
We do not need to follow this pattern, because video mode information is
provided by drm core. As a result most of the infoframe handling
code can be removed.

Start transmission immediately after detecting stream on HDMI lines
in irq_scdt() function without waiting for infoframe interrupt.

Signed-off-by: Maciej Purski <m.purski@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1511956130-24482-1-git-send-email-m.purski@samsung.com