dt-bindings: clock: Add bindings for Exynos850 sysreg clocks

System Register is used to configure system behavior, like USI protocol,
etc. SYSREG clocks should be provided to corresponding syscon nodes, to
make it possible to modify SYSREG registers.

While at it, add also missing PMU and GPIO clocks, which looks necessary
and might be needed for corresponding Exynos850 features soon.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Link: https://lore.kernel.org/r/20211217161549.24836-2-semen.protsenko@linaro.org