MAINTAINERS: add it66121 HDMI bridge driver entry

Add Neil Armstrong and myself as maintainers

Signed-off-by: Phong LE <ple@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210419071223.2673533-4-narmstrong@baylibre.com