drm/bridge: lt8912b: Add suspend/resume support

Add support for suspend and resume. The lt8912b will power off when
going into suspend and power on when resuming.

Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231115121338.22959-2-francesco@dolcini.it