PM / Domains: Drop genpd as in-param for pm_genpd_remove_device()

There is no need to pass a genpd struct to pm_genpd_remove_device(), as we
already have the information about the PM domain (genpd) through the device
structure.

Additionally, we don't allow to remove a PM domain from a device, other
than the one it may have assigned to it, so really it does not make sense
to have a separate in-param for it.

For these reason, drop it and update the current only call to
pm_genpd_remove_device() from amdgpu_acp.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>