drm/bridge/sii8620: set gen2 write burst before sending MSC command

Write burst should be enabled for MHL_INT_RC_FEAT_REQ and disabled for
other commands. The patch moves functions up and adds delay setting
for MHL3 burst mode.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1485935272-17337-15-git-send-email-a.hajda@samsung.com