ARM: dts: meson8: Use a higher default GPU clock frequency

We are seeing "imprecise external abort (0x1406)" errors during boot
(which then cause the whole board to hang) on Meson8 (but not Meson8m2).
These are observed while trying to access the GPU's registers when the
MALI clock is running at it's default setting of 24MHz. The 3.10 vendor
kernel uses 318.75MHz as "default" GPU frequency. Using that makes the
"imprecise external aborts" go away.
Add the assigned-clocks and assigned-clock-rates properties to also bump
the MALI clock to 318.75MHz before accessing any of it's registers.

Fixes: 7d3f6b53 ("ARM: dts: meson8: add the Mali-450 MP6 GPU")
Reported-by: Demetris Ierokipides <ierokipides.dem@gmail.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20210711214023.2163565-1-martin.blumenstingl@googlemail.com

arch/arm/boot/dts/meson8.dtsi

@@ -304,8 +304,13 @@ mali: gpu@c0000 {
 					  "pp2", "ppmmu2", "pp4", "ppmmu4",
 					  "pp5", "ppmmu5", "pp6", "ppmmu6";
 			resets = <&reset RESET_MALI>;
+
 			clocks = <&clkc CLKID_CLK81>, <&clkc CLKID_MALI>;
 			clock-names = "bus", "core";
+
+			assigned-clocks = <&clkc CLKID_MALI>;
+			assigned-clock-rates = <318750000>;
+
 			operating-points-v2 = <&gpu_opp_table>;
 			#cooling-cells = <2>; /* min followed by max */
 		};