arm64: dts: rockchip: Set RK3399-Gru PCLK_EDP to 24 MHz

We've found the AUX channel to be less reliable with PCLK_EDP at a
higher rate (typically 25 MHz). This is especially important on systems
with PSR-enabled panels (like Gru-Kevin), since we make heavy, constant
use of AUX.

According to Rockchip, using any rate other than 24 MHz can cause
"problems between syncing the PHY an PCLK", which leads to all sorts of
unreliabilities around register operations.

Fixes: d67a38c5

 ("arm64: dts: rockchip: move core edp from rk3399-kevin to shared chromebook")
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: zain wang <wzz@rock-chips.com>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Link: https://lore.kernel.org/r/20220830131212.v2.1.I98d30623f13b785ca77094d0c0fd4339550553b6@changeid
Signed-off-by: Heiko Stuebner <heiko@sntech.de>