drm/bridge/sii8620: Fix display of packed pixel modes

Current implementation does not guarantee packed pixel modes working
with every dongle. There are some dongles, which require selecting
the output mode explicitly.

Write proper values to registers in packed_pixel mode, based on how it
is done in vendor's code. Select output color space: RGB
(no packed pixel) or YCBCR422 (packed pixel).

This reverts commit e8b92efa
("drm/bridge/sii8620: fix display of packed pixel modes in MHL2").

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/1530204243-6370-3-git-send-email-m.purski@samsung.com