dt-bindings: gpu: mali-bifrost: describe clocks for the rk356x gpu

The Bifrost GPU in Rockchip RK356x SoCs has a core and a bus clock.
Reflect this in the SoC specific part of the binding.

Signed-off-by: Alex Bee <knaerzche@gmail.com>
[move the changes to the SoC section]
Signed-off-by: Michael Riesch <michael.riesch@wolfvision.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220209215549.94524-2-michael.riesch@wolfvision.net