PM / Domains: Do not check if simple providers have phandle cells

There is no reason that a platform genpd driver registered using
of_genpd_add_provider_simple needs to be constrained to having no cells
in the "power-domains" phandle. Currently the genpd framework will fail
if any arguments are passed with for a simple provider but the framework
does not actually care, so remove the check for phandle argument count.

This will allow greater flexibility for genpd providers to use their own
arguments that are passed in the phandle and interpret them however they
see fit.

Acked-by: Kevin Hilman <khilman@baylibre.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>