Add support for the graphics clock controller found on SM8250
based devices.

This is initially copied from the downstream kernel, but has
been modified to more closely match the upstream sc7180 driver.
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Tested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20200709135251.643-12-jonathan@marek.caSigned-off-by: Stephen Boyd <sboyd@kernel.org>