drm/rockchip: inno_hdmi: Drop custom fill_modes hook

Now that we have proper pixelclock-based mode validation we can drop the
custom fill_modes hook.
CRTC size validation for the display controller has been added with
Commit 8e140cb6

 ("drm/rockchip: vop: limit maximum resolution to
hardware capabilities")

Signed-off-by: Alex Bee <knaerzche@gmail.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20231222174220.55249-27-knaerzche@gmail.com