mips: configs: ci20: Enable DRM_DW_HDMI

Commit 4fc8cb47 ("drm/display: Move HDMI helpers into display-helper
module") turned the DRM_DW_HDMI dependency of DRM_INGENIC_DW_HDMI into a
depends on which ended up disabling the drivers in the defconfig. Make
sure it's still enabled.

Fixes: 4fc8cb47 ("drm/display: Move HDMI helpers into display-helper module")
Reported-by: Mark Brown <broonie@kernel.org>
Reported-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>