drm/bridge: tc358762: Split register programming from pre-enable to enable

Move the register programming part, which actually enables the bridge and
makes it push data out of its DPI side, into the enable callback. The DSI
host like DSIM may not be able to transmit commands in pre_enable, moving
the register programming into enable assures it can transmit commands.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230615201902.566182-1-marex@denx.de