drm/vc4: Fix DSI T_INIT timing.

drm/vc4: Fix DSI T_INIT timing.

The DPHY spec requires a much larger T_INIT than I was specifying
before.  In the absence of clear specs from the slave of what their
timing is, just use the value that the firmware was using.

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: http://patchwork.freedesktop.org/patch/msgid/20170627195839.3338-2-eric@anholt.net
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>