phy: rockchip: samsung-hdptx: Restrict altering TMDS char rate via CCF

Although, in theory, the clock provider functionality could be enabled
as a standalone driver feature, in practice it is unlikely that it would
be ever needed separately from the common PHY related features, i.e.
making use of the PHY PLL as an alternative and more accurate clock
source for display modes handling. Which means the PLL will be always
programmed according to the TMDS char rate set via the HDMI PHY
configuration API.

Currently it's possible to freely adjust the rate via the clock API as
well, that is through clk_set_rate(). Making the clock read-only is not
feasible since we need to ensure any rate update done via the PHY
configuration API has been actually programmed into the hardware before
CCF accesses it. This would be normally done during phy_ops.power_on()
or clk_ops.prepare() callbacks, but it might happen that the former gets
fired too late and the latter only once, hence we need to keep handle it
via clk_ops.set_rate() as a fallback approach.

Prevent changing the TMDS character rate via CCF by letting
rk_hdptx_phy_clk_round_rate() always return the value set via
phy_configure(). To avoid breaking existing users, i.e. RK DW HDMI QP
bridge driver, until the switch to the HDMI PHY config based approach is
completed, introduce a temporary exception to the rule, toggled via the
new ->restrict_rate_change flag, which indicates whether phy_configure()
has been called or not.

Additionally, revert any unlikely rate change that might have occurred
between the calls to ->round_rate() and ->set_rate().

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Link: https://lore.kernel.org/r/20250318-phy-sam-hdptx-bpc-v6-11-8cb1678e7663@collabora.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>