MAINTAINERS: update files for Amlogic DRM Driver

This patch adds the dw-hdmi bindings and RST kerneldoc to maintained files.

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1491308131-22071-2-git-send-email-narmstrong@baylibre.com