drm/meson: dw-hdmi: Enable the iahb clock early enough

Instead of moving meson_dw_hdmi_init() around which breaks existing
platform, let's enable the clock meson_dw_hdmi_init() depends on.
This means we don't have to worry about this clock being enabled or
not, depending on the boot-loader features.

Fixes: b33340e3 ("drm/meson: dw-hdmi: Ensure that clocks are enabled before touching the TOP registers")
Reported-by: "kernelci.org bot" <bot@kernelci.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Tested-by: Guillaume Tucker <guillaume.tucker@collabora.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
[narmstrong: changed reported by to kernelci.org bot]
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201120094205.525228-3-maz@kernel.org