PM / Domains: Remove unusable governor dummies

The governor dummies for the !CONFIG_PM_GENERIC_DOMAINS case are
unusable, as a governors is always referred to by taking its address,
which you can't do with a literal NULL pointer.

I.e.

	pm_genpd_init(genpd, &simple_qos_governor, false);

fails to compile with:

	error: lvalue required as unary '&' operand

Hence just remove the governor dummies.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>