soc: ti: Mover power-domain drivers to the genpd dir

To simplify with maintenance let's move the ti power-domain drivers to the
new genpd directory. Going forward, patches are intended to be managed
through a separate git tree, according to MAINTAINERS.

Cc: Nishanth Menon <nm@ti.com>
Cc: Santosh Shilimkar <ssantosh@kernel.org>
Cc: Tero Kristo <kristo@kernel.org>
Cc: Tony Lindgren <tony@atomide.com>
Reviewed-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>