drm/bridge: lt9611: Switch to atomic operations

Use the atomic version of the enable/disable operations to continue the
transition to the atomic API. This will be needed to access the mode
from the atomic state.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dave Airlie <airlied@redhat.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220331153923.14314-1-marex@denx.de