drm/vc4: hdmi: Prevent clock unbalance

Since we fixed the hooks to disable the encoder at boot, we now have an
unbalanced clk_disable call at boot since we never enabled them in the
first place.

Let's mimic the state of the hardware and enable the clocks at boot if
the controller is enabled to get the use-count right.

Cc: <stable@vger.kernel.org> # v5.10+
Fixes: 09c43813 ("drm/vc4: hdmi: Implement finer-grained hooks")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>