drm/bridge: dw-hdmi-qp: replace mode_valid with tmds_char_rate

drm/bridge: dw-hdmi-qp: replace mode_valid with tmds_char_rate

Replace .mode_valid() callback with .hdmi_tmds_char_rate_valid(). It is
more generic and is used in other mode validation paths. The rate
validation for .mode_valid() will be performed by the
drm_bridge_connector code.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241130-hdmi-mode-valid-v5-9-742644ec3b1f@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>